I've spent something like 10 hours with it so far, I am pretty hooked.
My only complaint so far is that the in-game currency generation is far too low. Buying 1 pack of cards is 100 gold, you get 5 gold for 5 wins against other players (through random mode, there are no prizes for playing people on your friend list). So you need to win a loootttt of games for 1 pack of cards. There are also "daily quests" you can do that generate gold, but, so far it seems you only get 1 quest per day (granted this is only the second day of me playing, could be random for all I know).
That said the problem with it is I don't think spending gold on packs of cards is worth it anyway. You can do the arena mode for 150 gold which gives you 5 rewards after losing 3 games. The awards are based on how many games you won, but, so far every time I have gotten at least 1 pack of cards anyway. Plus the mode is more fun than just random battles anyway.
Otherwise I am loving everything about the game, but, I am not someone who plays other card games so I can't really compare it to anything.