Card Hunter is now on Steam, free to play with cash shop (same as in browser). The new sci fi-themed Expedition to the Sky Citadel expansion is also live, free unlock once you’ve completed the main campaign, with free loot daily for launch week.
The Steam client seems less responsive than the in-browser client. [ETA: I was wrong. The game is now running more slowly in the in-browser client as well. It is a problem with the game, not Steam.]