To me, a few things, not in any order of importance, just in order of me thinking them up:
1. It's an RTS with no set maps. I never know what kinds of setups the whole thing is going to fling my way, so there's no way to go into it thinking "Well, okay, that place over there did me in last time, so I just wont go over there yet". You cant beat a map in this game by just memorizing it, which you can in other RTS games. The fact that it's an RTS with LOTS of sub-maps then crowded into that overall "map" is another huge aspect of this.
2. Lack of micro. I'm sorry, but I look at something like StarCraft and I do not see "strategy", what I see is players trying to see who can hit buttons the fastest. Hell, it almost looks like they're trying to play a fighting game on a keyboard. Ridiculous. But with AI War, even when I want to be in direct control of a fight (and with my playstyle, this is pretty frequent), even then, I can pause at any time, and look around, and give orders while paused. Or just slow down time and do it that way. It remains apparent throughout the entire thing that no matter what, the strategy always comes first.
3. Possibilities, and the way things affect them. It's one thing to have maps that are overall randomized. But then you have things like the AI choices... just choosing different ones, that thing alone causes huge changes within the game. It can affect what goes into the maps, it can affect how those things are used by the AI, it can affect how the player approaches those things... it's one tiny selection on the starting menu, but it changes so very many things. There's a lot of options that do this, with this game.
4. Lots of approaches. This honestly is something that I've found true about all of your games, for the most part, is that there's usually tons of different ways to approach any given situation. There's rarely one "right way" to do something, with Arcen games. Or at least, that's been my experience. With a lot of normal RTS games, when you're playing in singleplayer, there often IS a single "right" way, and then tons of "wrong" ways. Even just when fighting against the AI in a skirmish mode, since the mechanics and such are usually very stagnant, there's still often just not that many possible approaches. In your games though, this is rarely the case, if ever. Even something like the first Valley had this, which I think is one of the things that brought me here. AI War is particularly good at it. I have my own unique playstyle (very defensive, with a high focus on using Champions to augment my fleets when attacking), and the game supports the possibility of all sorts of playstyles. I know I'm listing this at number 4, but this is a really huge thing for me. It's something often seen in roguelikes too, which is where I got my appreciation for it, I guess. In AI War though, it really shines. BD is another one that's just fantastic about this.
5. LOTS of things to do. There's all sorts of goals to go after, all sorts of enemy installations to attack.... and each one of these things to go after or do is DIFFERENT. And then each has it's own strategic impact. With a lot of RTS games, they honestly lack this. You go through a "get resources" phase, a "build up the start of your base" phase, and then a "destroy the enemy base" phase. Well, it doesn't work like that in AI War. Hell, when you "destroy the enemy base" you then realize that the enemy still has 79 bases remaining. So that alone is not going to be enough, and you CANT just clear all of them. So it leaves you thinking, what do I do next? Do I go after this thing over here? How about that special research thing, that has a particular tech that I already know I find useful with my playstyle? Or should I hit this system over here, that's starting to look like a real danger to my own that borders it? Or do I try to do some hacking, and the setup that this entails? Or maybe send out my Champion to one of those special zones to level up, to support future attacks? And then even better is the fact that you can do multiple things at once. I don't JUST have to focus on one thing at a time. I also don't have to do any of them in a specific order. Again, all of these things are things I associate with Arcen games as a whole. Regardless of which game of yours I'm playing, it has this to some extent. Well.... Shattered Haven may be the exception since that was more about figuring out very specific solutions. But other than that, pretty much all of your games do this in their own way, and it leads to them fascinating me to no end. I like it when games force me to make interesting decisions that really affect things from a strategic/tactical point of view, rather than just saying "go do these things in these orders, and here's some Goombas in front of you to be annoying".
6. LOADS of content. Seriously, there's a really stupid amount of content in AI War. Even just the base game... you're given a zillion things to play around with.
7. .....but you don't HAVE to use any of it. Like those Champion units, I really like those guys, that's one of my favorite things from any of the expansions. But like absolutely everything else in the game, they can be turned off if the player doesn't want to use them, wether they don't like them whatsoever, or just want to try a particular run at the game with some changed options from what they usually do. This also really helps for learning the game at your own pace. You can keep the crazier-sounding things off, and then slowly turn them on as you keep learning and playing more.
8. The AI does really interesting things. I never know what it's up to. It's not going to be at all predictable, which it is in most RTS games. This seems to be one of the things that this game is most known for.
9. LOTS OF UNITS. I never feel like I don't have enough units or structures to accomplish stuff.... other RTS games ALWAYS give me that feeling, but not this one. I can have a zillion different things at once. It ends up becoming a question of SHOULD I build such and such thing, rather than CAN I build it.
10. Asymmetry. I really wish more games of this sort did this. This makes things extra fascinating to me, and it means that it wont feel like a "mirror match" also. I'm not fighting against JUST the units that I myself can also use. Sure, I'll definitely see some of them on the enemy's side... but at the same time the AI has it's own unique threats that I cannot use, and the same the other way around.
I'll stop rambling here. But I think you get the idea. Probably.
