Card Hunter [official site] is available on Steam right now. It will be one of the best games released on Steam this year just as it was one of the best games of 2013, when it launched as a browser-based free-to-play CCG/RPG hybrid. The development team includes former Irrational, Popcap, Looking Glass and Magic: The Gathering folks and the game is every bit as good as their combined back catalogue suggets it might be.
Go. Play it now.