I've recently taken quite a liking to KeeperRL, a surprisingly good mix pulling in features from dungeon building, exploration and roguelikes to make quite an engrossing game. The developer also recently put out Alpha 24.
Depth of Extinction is a retro-inspired turn-based tactics game, it's a little like XCOM with some rogue-lite features thrown in and it's getting better all the time.
It seems my recent article about Valve removing the link to the Steam Machines page caused quite a stir, so Valve have now confirmed their continued support for Linux gaming.