My current poisons are:
Frozen Synapse [http://www.frozensynapse.com/], a top-down simultaneous turn tactics sim, where you can watch projections of your orders before commiting to them. It also features a pretty nifty sci-fi storyline which isn't about "science is evil". More like "corporations are evil". You, the player, are a cyber entity yourself. Oh, and a cool electronica soundtrack sets the tone there.
Shadowgrounds [http://frozenbyte.com/games_shadowgrounds.php], a top-down survival shooter thing in the traditions of Alien Breed. It has also some levelling elements in the form of weapon upgrades, some interesting light mechanics, sort of destructible environments and a hamster that plays chess.
Terraria [http://www.terraria.org/] is like 2d minecraft, except with more stuff. It may not have railways and redstone circuits, but it does have meteors, NPCs, special areas and boss monsters. It was released a bit before the intended date, so it's going to get content updates. In fact, the original plan was to provide more content after release anyway. Because of the 2d framework, adding new stuff is easy.
Liberal Crime Squad [http://lcs.wikidot.com/]. I think I've talked about this game here already. It's a brutal political activist game, where you can gain support for your liberal cause by killiing conservatives. Right now I'm trying to do a pacifist run, with my main guy constantly wearing a ninja costume, sneaking into buildings and stealing secret documents to expose the conservative scum.
All this mainly to avoid working on my coursework. I hate myself somewhat.