Yeah, Hearthstone is real casual compared to most other TCG games, mostly because it is designed around fast and short matches with very basic and easy to learn mechanics.
Magic, whcih after all this years is still the "boss" among card games, is very complex and that may even be the reason why so many are drawn to Hearthstone. hearthstone is easy to play, Magic is tricky and takes a lot of time to learn all the different mechanics and stuff, esspecially since this stuff is NOT explaned directly on the cards itsels. For example flying units. On cards they are only tagged with the word "flying" and if you don't know the rules you wouldn't understand that they can only be attacked by other flying units (or ranged units which are also not explained ont he card itself). On PC versions this is of course a little different since pop-ups explain the different card abilities when you hover over them.
Now about what makes TCGs fun for me. I think mostly the collection aspect and the varity. I like to collect stuff. A lot of stuff. I was a huge fan of Banjo-Kazooie on the good old Nintendo 64 and I wasn't satisfied until I collected every single piece in the game. I remained this behviour when I joined Steam. I collect as many achievments as I can on games. Trading Card Games ae centered around collecting stuff, in this case cards. I buy boosters not because I want strong cards but because I just want NEW cards.
This also combines with varitiy. I need varity in games, I cannot do the same routine every time I play. While you can say card games also are centered around the same gameplay (you start a game, you play cards, you try to decrease your opponent's health points to zero), the matches themself are always different. You don't know what your deck your opponent has or what cards you will draw. This adds to the thrill of the game, not knowing what will happen next. Sometimes you course the randomness because you picked the wrong card from your deck, sometime you draw exactly what you need and are happy.
Then there is the skill requirement that Misery mentioned. How do these type of games require skill when they are luck based on what you get from boosters and what you draw in matches? It's used nt he way that you try to minimize the luck amount you need in a match. You create decks with the little you have. It's not that you need the best cards but use what you have in the best way you know. Putting the rigth cards in your decks will minimize the chance o drawing stuff you don't need. Picking different cards that work perfectly together if you can use them (Synergies) will help you in the later matches. planing your strategy before actual matches can be pretty fun.
However, maybe , Cyborg, you are interested more in this kind of card game:
http://store.steampowered.com/app/337150/Thats the digital adaption of "Sentinels" of the Multiverse", a very popular cooperative card game. It's NOT a trading card because it features no collecting or trading to begin with. The game is also aviable as real card game, not a pc game (if you prefer to play it like this).
The game is really really cool and I can only recommend it. I got it in some bundle and didn't care for over a year because I bought the bundle for something different but when I finally started to play the game I regretted that I ignored the game so long.
The gameplay is a little hard to descripe because it's not a tgc game but behaves similiar to one. In its core its a cooperative game that you play with friends. Each player plays one or more super hero (most heroes are inspired from classic DC and Marvel heroes but were invented for this game) and each hro has his own deck. You cannot modify the deck in any way, the deck has a fixed amount of cards and all cards are tied to that hero. So tehre are no booster packs you can buy, however you can buy complete expansion packs with new decks.
The players figth against a villain, also represented in a deck that was specialy designed to him. The decks represent the abilities and equiment of the heroes and villains they belong to. For example, the hero Absolute Zero creates, like his name assumes, has temperature control abilities, mostly ice (but in some cases also fire). In other words, he can freeze enemies with ice beams. He "absorbs" also all ice damage he would sustain, making him an effective tank and damage dealer.
Players play in turn one card each turn and a power (every hero has a special ability but can also get new powers from played cards), after that they draw a card ( at the END of the turn, not at the start like in other card games). The villain is represented through the game itself, no player controls him. Instead he plays the top card of his card and resolves the effect mentioned there.
The goal ist that the players combine their heroes and defeat the villain together. All villains (ansd also heroes) have a two sides and when the conditions are met, you flip them. Heroes flip when they are defeated and they can use the abilities mentioned there but are not allowed to use any cards anymore, villains get or loose abilities when they flip but flipped villains are not defeated, its just a different form of the same villain. For example the villain "Citizen Dawn" plays a creature oriented deck. She plays a lot of minions on her first turn and adds many more each turn, when you kill too many of them she flips too the other side and is invulnerable until there are enough minions on the field again.
When a player is defeated, he can still play but use only he three abilities mentioned on the backside of his hero card. The game is only lost if ALL heroes are defeated. Some villain decks are stronger/harder than other villains, representing stronger villains of the fictional world in this game.
For additional varity each game is played on a different terrain, the environment. The environment has its own deck and can affect both villains and heroes positivly and negativly. Like the villain it plays itself, just reveal the top card and resolve the effect.
If you have Tabletop Simulator you can play the game on PC without having to buy the digital version, the digital version is however more convenient because it resolves all the effects, buffs and debuffs automatically and you don't have to do all the math in your mind (which can be really painful for the more complex decks in the game).
If you decide to buy the digital version or even the printed version, buy also the expansions. I know I risk getting lectured by chemical_art again that I sound like a bot trying to sell something but in my opinion the true fun of the game starts when you have access to ALL decks of the game, not just 10 (not counting environment and villain decks). The base game however has some really good and interesting hero like Legacy (support hero with a lot of buffing abilities that affect other heroes), Absolute Zero and Visionary (control deck, messes with the villain deck so it's not luck based anymore what the villain draws/plays).
The villains of the base game are however not very interesting, the more interesting ones are n the expansion with unique play styles (I hate and love Spite because he flips the entire concept of the game and makes it to a cat and mouse scenario where he chases after civilians that you have to save).
Okay, long monologue about stuff that people propably won't even read, so I sum it up: TCGs are fun because of collectibles and strategies, Sentinels of the Multiverse removes the entire "pay to win" part of such card games because you have fixed decks and play with other players together instead against them.
