Into the Breach is a new strategy game from the makers of FTL. I say new because it just got a Mac release, but it has been out on Windows for a few months now.
So far, this is my Game of the Year.
The gameplay is centered around a “chessboard” of terrain, where aliens keep showing up and you have three units to try to kill them. The aliens try to destroy buildings, and you have to stop them. Killing them is a way to stop them, but not the only way - pushing them out of the way works fine. If you lose, you get to try again, with some of the experience that you gained last time (time travel shenanigans). The result is something in between a strategy game, a puzzle game and an RPG - an RPG written by the lead writer of Fallout 2, at that.
I cannot recommend this game highly enough. I am enjoying myself immensely, and my only wish is that I could have it on the iPad too.
It is currently 20% off on Steam.