I've been playing Into the Breach (PC), from the creators of FTL. It's a little turn-based, grid-based strategy game that reminds me a bit of the original, 1994 X-COM crossed with Worms. Each "mission" consists of an 8x8 grid that you deploy your three mechs (which you customize with weapons, upgrades and pilots) to. Each mech can move a number of spaces and then use its weapon once. When your turn ends, the aliens get to do the same and attack either the buildings that you're supposed to protect or your mechs. You can see their upcoming attacks during your turn, though, so you can decide which to neutralize and how.
Each of your turns is like a little puzzle in which you have to use your moves and weapons very wisely, since there are usually more aliens than you have mechs and losing only a few buildings can result in defeat... and the game is a bit like a rogue-like in that losing a pilot means losing him forever and failing even one mission forces you to start the game over. The missions typically last only 5 minutes or so, though, and you could do a whole playthrough of the game in one night, if you wanted and if you can avoid failing any missions. The missions are randomly generated, so there's a lot of replayability.
Anyways, I'm really enjoying it. It's very simple, yet also quite complex and requires you to think. It's also a perfect little game to play in spurts, such as when you have only 10-30 minutes to play. I recommend it if you like turn-based strategy and/or puzzle games (and, especially, if you're fond of X-COM or Worms).
(Heh. It looks like I'm advertising the game, but that's what this forum engine produces when you simply paste a link to the game's Steam page.)