I'm also a kickstarter backer for HEX TCG but it's still in alpha but Hearthstone has much more polish (and more importantly) can easily be played by kids. Where as HEX requires more thought into deck builds as you need to have resource cards (like pokemon)
scrolls is really good to since you play the cards on a battlefield like a turn based strategy game.
it's not free though but I found it far more fun than hearthstone and getting cards doesn't take an age since you get a reward each game whether you lose or not , obviously the victor gets a greater reward.
there's also card trading in a trading card game amazingly.....
someone even made an auction house mod for it.
made by the minecraft guy and seems a lot more complicated than it is, although it can take a while to understand the synergy between some cards that can make OP combos if you can pull them off ^_^
each deck can have multiple strategies as well.
like decay can do a poison deck , a rush deck , a card recycle farm deck , a zombie hoard deck etc rather than each deck type being limited to one specific play style or you could just do a trick deck for an op combo and hope you manage to get what you need out and pull it off.
for example part of my trick deck is
enchant it with this spell
stick one of these next to it
stick this enchant on the construct or watcher
= perfect synergy
LOL as you want your units dead more than the enemy does
.
even without the watcher you can do it with 2x animovre on the construct and for every one of your units that dies next to the construct ,you get 2 cards so you can end up with your whole deck in your hand which is stupidly fun
hard to pull it off though as most people see a wall go down and try to kill it before you get the HP up but it's awesome fun
you can also mix the different deck types as well and some of the cards have synergy to encourage it but that does get really complicated
totalbiscuit is total fail at it though.. like putting artillery peices down where they would hit where someone is standing IF it fired that turn rather than putting it somewhere to protect a lane someone could move to