Guild of Dungeoneering [Steam store page]
Some of the mechanics are unconventional, but once you learn how to play it properly it's a fun and well balanced dungeon crawler with a twist. It's one of the only rogue-like dungeon crawlers that I actually go back and replay from time to time.

Dead Man's Draw [Steam store page]
I really enjoyed the amount of variety in this single-player card game. There are some really unique card mechanics that keep it fresh and challenging.

A survival card game with an interesting concept, but the flawed mechanics make winning more luck than skill-based.