Allright. This might be long, because anything from me always is, but you typically dont seem to have any issues with that at all, and you DID ask, so here I go... I'll try not to mangle this too much.
Let me start off by saying one thing: I really, really cant recommend this game enough (and yes, you want "rebirth", as was said before, not the original; the difference is... possibly the most dramatic difference I've seen in a piece of DLC in YEARS). I consider it one of my all-time favorites, which isnt something I say lightly, particularly considering the downright stupid number of games that I own. And it's worth noting that I typically DONT like games where the RNG is what determines victory or defeat. Like in, say, FTL; I ended up not playing that all that much because of how the RNG was handled. When you get to an event, you're given choices in a dialog box, and when you pick one, you get a result, of course. If you get a BAD result... there's *nothing* you can do. If the result was "one crew member dies"? Sorry, he's gone, and no amount of actual skill will prevent this. You cant like, dive into some desperate battle to save him or something like that. Not in that game. And I *hate* that sort of thing, despite loving procedural generation, which as you know is one reason why I get into your games as well.
Now all of that being said, hmm, a bit about the game itself...
As you know, it's basically Zelda + a roguelike with a seriously stupid amount of content, and also with some shmup elements added. Quite a ton of the old elements from the original Zelda game are in here, from the treasure rooms, to the shops, and even those funky "basement" rooms where, in the very first game, items were held. And of course things like bombable walls and secrets (more on those later), and even a ton of items from Zelda directly exist in this game, and do exactly what you should, from the compass to the blue candle or whatever. The exploration aspect of Zelda is always here as well; a big part of the fun of Zelda, or of any roguelike as well, is the exploration. I looooove exploring new areas, and finding unexpected cool stuff, and this game is fantastic about that.... IF you know what you're doing. But more on that bit later as well...
Of course, one of the big differences is the way the game plays. Zelda has you stab your enemies, occaisionally using a sub-weapon from a distance maybe, but not very often. Isaac has you shoot things instead.... but not always.... and a great number of enemies have ranged attack patterns as a result, which means that chances are, there's SOMETHING in the room shooting at you, often while something else tries to run up and bite your head off. This is one thing the game does very, very well: no matter just how screwed up Isaac gets (as in, with very bad item combinations) there *is* a way to defeat everything, and win nonetheless. You can always, always use skill to overcome everything else. Learning enemy patterns is an absolute must, and there's TONS of them, which are all quite varied, though there are definitely some that are more rare than others. When you're just starting out, things wont be too tough. The difficulty level, even if you choose hard, is set low for some time; you actually unlock the "full" difficulty as you advance through the game. If I recall correctly, the max difficulty is achieved by the time you defeat It Lives for the first time (and yes, that's a dumb name for a boss). It takes awhile to reach that point for the first time, as it involves beating the Heart 10 times first.
What makes it interesting is the items though. These can completely change how things work, and the game is famous for it's synergies. There are, of course, ways that you can break the game. But I've never found a roguelike that DOESNT allow this... it's just that, in this one, it's alot more fun to do. It doesnt happen nearly as often as you'd think. And some of them can actually pose a threat if you're not careful; I had one setup recently where, by the end of the game, Isaac was firing tears (bullets, whatever) that were so bloody huge that they literally took up the whole screen. Needless to say, it was easy to hit things. But they also COVERED EVERYTHING. I couldnt see anything else while they were still onscreen. I did win that run, but I nearly wrecked myself because I wasnt really adapting to that very well. And that's part of the fun and challenge, is that the game will just keep DOING that. Even after hundreds of hours, I still, rather frequently, end up with very strange setups that I've never seen before, that are doing something seriously screwy, and that are requiring me to adapt and approach situations in very unusual ways. Other roguelikes, they dont do this. Once I've mastered one.... it wont put up much of a challenge to me anymore. I mean, most of them will still be tough, but I usually hit a point where I *will* win every single time. And not just win, but win without coming close to losing. This game doesnt have that issue. It's one of the things that keeps me glued to it. I might have runs where I'm all sorts of tanky and can do things like just run over rocks/walls and just CRUSH them, not even needing to fly over them, yet my attack is kinda weak or very strange, so even though I *can* take alot of hits without dying, if I'm not careful anyway, I *will* take alot of hits. Or even runs where I might be just annihilating bosses in a single monstrous blast; I've had even runs like that go bad. You'd be surprised at just how things can work sometimes.
What makes it all work though isnt the number of items, or the crazy synergies, or the procedural everything. It's actually the fact that the RNG does *not* control your chances of winning. Often, with a game like this, the perception that many people have is that it's too random, skill wont matter, the RNG alone will decide how you do, blah blah blah. That's not so here. There will definitely be plenty of RNG. But Isaac is a game about making decisions, and this forms the absolute core of your run. There's no element in the game that is more important. Obviously, yes, you need to deal with combat and use skill and such to defeat your foes.... but HOW you go about this will be decided by the decisions you make and the actions you take in relation to those. For example, you open up a treasure room, and bam, just like Zelda there's an item there to be picked up. In Zelda, you'd just grab it, definitely. In Isaac, this is bloody stupid. When you encounter an item, you have a decision to make. Do you take it? Do you NOT take it? Sometimes, grabbing even what often is beneficial can be the thing that undoes your run. Choosing carefully is very important. Generally, you make choices based on your current build, your current strategy, current active item and numbers of consumables, and even other things you've spotted on that particular floor. Make the right decision, and you'll get stronger, or gain some sort of other benefit. Make the wrong decision, and you might explode alot, or who knows what else. The interesting thing is that it's not just "take or do not take" as the options available. Often, there's a whole pile of other options. Very often, I'll enter a treasure room (or whatever), spot the item.... and just leave it there. It's not that I wont take it; it's that something else is influencing that decision. Perhaps I have the D6 or another item that can re-roll items like that. Perhaps I want to use some specific effect I already have a few times more first, having spotted a few batteries around the floor, yet not having USED them yet because I wanted to see what was in the treasure room first. Or.... all sorts of other reasons.
Which is another thing. The more you learn about the game, the more info you will have to make decisions with. When you're first starting out, you'll probably just grab everything to see what happens. You'll experiment alot, which is important. But as you learn what more items do, and start to learn how other things work, such as secret and super secret rooms (rooms entered via bombing through walls; there's one of each on each floor, and they're actually NOT completely randomized; the game uses specific logic to decide their position, and using that knowledge, you can deduce their most likely locations), or perhaps special actions you can take based on things you've spotted around the level, you'll start to have more and more info that factors in, and you're suddenly less about just choosing at random or just "because", but instead choosing based on all of these other things you know, which dramatically reduces any effects that pure RNG can have on you. Where I'm at, I look back on the game, and I cannot honestly say that the RNG has ever killed me purely on it's own. Not once. It can make things hard, or it can sometimes make them easy, but in reality, it's all based on MY decisions and actions based on what I encounter during my runs, and what I do with those things that I encounter. And this is something I love about it; alot of roguelikes actually have trouble with this, and there are plenty of them where the RNG, and the RNG alone, can kill you no matter what you do. Again, I hate that sort of thing. But this game simply doesnt do it.
Now, that being said, the game has a bit of a mean learning curve. Alot of players are REALLY DAMN HAPPY when they defeat Mom or the Heart for the first time, because they probably had great trouble getting to those.... despite that those are NOT the final bosses, and much worse things wait beyond them, once you unlock the areas past there. But the learning curve means that getting there just is not at all easy early on. You *will* have alot of stupid deaths, and at times, it will probably seem like the RNG alone got you. But no, there's ALWAYS something you COULD have done to have overcome whatever took you out. Like in any roguelike though.... you need enough info and enough skill to manage to DO it, and to recognize it for what it is. The game can be pretty frustrating for new players. Something tells me though that you specifically dont really mind that sort of thing though. Heck, your own games certainly have tough learning curves, but they work out very well in the end. This one, to me, is the same.
Now, there's actually alot more to it than even just that. Seriously, this is a *deep* game. Hundreds of hours in, and I'm still learning new things. But it'd take me seriously forever to explain much of it here; everything I've said here only looks at the basics. As I said though, there is depth here. Lots of it. It's one of the reasons why I can recommend this so highly.
Not just depth though.... but also content. Yes, there IS overall progression in this. A seriously stupid amount of it. Almost TOO much. There's a huge number of things to unlock, both characters, items, entire new areas, and even bosses. So very, very many of them. And tons and tons of things just even when you start out. Hell, in total, the game has over FIFTY seperate bosses in it. That's.... alot. And when you also consider "champion" versions of bosses, and also room layouts, even a fight with the same boss can be very different from one game to the next. There's a big difference between fighting Monstro in a normal open arena, and fighting four bizarre little red hyperactive versions of him in a room with rocks and holes in a funky layout. There's an equally stupid number of enemies in the game, and some damn silly number of items right now; 350+, I think it is? And we're near the point, FINALLY, when Afterbirth will come out, which'll add some damn silly amount more to it.
Even just something like room layouts.... I theorize that there are AT LEAST a thousand different room layouts in the game that can appear. SO many hours in, so many times through the game and through each possible area, and I still, quite frequently, am finding rooms I've never seen before. And heck, for Afterbirth, the expansion, the developer has already stated that JUST in there, there are over 1000 *new* rooms being added. Which I should have also mentioned; the game generates the FLOOR procedurally, but the actual contents of the rooms are not. It's like how you guys did the building interiors in Valley Without Wind. Which really does work out much, much better than "pure" procedural generation. You'll start to recognize certain rooms as you go, and have an idea as to what you might want to do about them based on your current build and amount of things you're carrying.
Now, I could ramble on.... and on.... and on.... about this. I really could. But at this point, if you want to know more, it's best to just ask questions about it, as if I keep going any further, this will start to get confusing.
I will though point out a couple of the game's DOWNSIDES, as it wouldnt be fair not to.
The biggest and by far the most goddamn obnoxious downside.... at first.... is lack of information. This always bugs the hell outta me. Now, to be fair... MOST roguelikes do this. I mean, seriously, this is SUCH a common problem that it's just even MORE obnoxious. But this game, yes, has the issue. When you grab an item, sometimes it may tell you just what it does. It may say something like "DMG up + range down" or "Homing Shots". But other times.... it wont. Like, when you pick up "Bob's Brain" the first time (and it probably wont be long before you encounter this one), the description is "explosive thoughts". A big green floating brain will then follow you around. Of course, the usual reaction to this is "WTF???". And chances are, you'll find out what it does.... when it violently explodes in your face. Had you been given a full, proper description of it, you could have avoided that! But like in many roguelikes, that just aint happening sometimes. And of course there's some items where not only will it not tell you, but it wont do something obvious like explode or spray lasers everywhere. Like, there's an item called "A Lump of Coal", which is a pretty common one, and generally desirable. But it wont tell you how it works. The description? "My Xmas Present". Basically what it does is that, the longer your shots travel away from you before hitting a target, the stronger they get; the optimal use is to fire from a long range. You can really do some big damage this way. But that wont be obvious when you first get it... you may still be trying to fight up close, and not getting an idea as to what it's REALLY doing. And there's a few items that are even MORE confusing, where the confusion can be outright annoying. The trinket (trinkets being non-permanent passive items, you can hold one at a time) called "Mom's Toenail" just says "
" when you pick it up. It wont appear to do anything at first. Until, suddenly, it does (and with that one, you discover NOT to pick it up, most of the time....).
I find that items and such are easier to learn in this game than in many roguelikes (and there's a site that helps ALOT, which is platinumgod.uk, I have this site open in my browser whenever playing this, since my memory is so bad), but still, the issue is annoying.
The other one is the act of unlocking everything. It takes a long, long time to 100% this game. And that's fine! This game is built for extreme replayability. Most players dont stop at all even after they've finally gotten everything. But good luck getting there! Some things can be.... seriously irritating to get. Wether they be achievements (I'm not even going to describe how much I hate the Bandage Girl one, because I'd end up breaking something just thinking about it), or specific item unlocks. The biggest and most infamous example, and one of the single most goddamn annoying and irritating things I"ve seen in a game in a very, very long time, relate to a character named The Lost. I hate this guy. I hate him so much. Everyone hates him. EVERYONE. I doubt there's even one exception to this rule. The lost is designed to be "a challenge, even to long-time veterans". What does he do? Simple: he has no health. Literally. Not a single heart. He cannot GRAB any either, regardless of the TYPE of heart. He dies in one hit. He will always die in one hit. The ONLY things that can prevent this are items that grant some sort of invincibility at times, or that cancel out attacks somehow. Items that give you more heart containers? Bosses will still happily drop them upon defeat... but they have literally no effect on this guy. None at all. And Isaac is not an easy game. All sorts of dangerous things everywhere, shooting and lunging at you.... and the TINIEST mistake just ends your run with this guy. That's not enough though, no no no. See, the developer, in a fit of PURE SADISTIC EVIL, locked the game's strongest items behind this character. Every character has 6 unlocks that are bound to them, which involve beating specific bosses and paths, and doing the boss rush successfully. Because ARGH, The Lost has these same things. Except they're damn near impossible to get. For me? It's too much. I cant do it. I usually cant get this guy past the Caves. This should say something about it, really... In the end, I decided to just say "screw it" for that character, and just pretend he doesnt exist. Which is better than spending hundreds of hours on JUST HIM to unlock stuff (and while the stuff he unlocks is STRONG, it's not particularly INTERESTING, in an "is this fun to use and mess with" sort of way).
I'll stop there before this becomes an angry rant about that stupid character. But yeah, those are what I see as the game's downsides. But since everything else is so GOOD.... they're VERY outweighed by the good stuff.
So, there, that's my long-winded and hopefully not too confusing description of why I think this game is so freaking good. Again, I really cant recommend it enough. And if there's any questions at all, just ask. At this point, I seriously know *alot* about it. I can definitely say "I know what I'm doing" with this one.