Alien Swarm There are aliens. Swarms of them. You have to kill them. Oh, and it's free, and it's made by Valve.
This looks like a blast. Downloaded it and ran a bit of the practice level. It's got a very L4D feel to it, but you level up and kill lots of bugs.
Played this back in the UT2004 days. Pretty damn fun. Gotta love Valve, the only company who is awesome enough to give out free games with no bullshit while everyone else is busy gouging people on DLC and map packs.
Played a few levels last night. Freaking amazing, can't wait for the modder community to bring out some badass new campaigns.
I dig it! Short but sweet. I'd definitely be interested in additional campaigns, though I wonder if it'll be a "the first one's free, pay for the rest now that you're into it" affair. Played through on normal and hard, haven't tried insane just yet.
Everytime I get into this game, even just for practice, it's really laggy. It is, however, pretty fun when it's not.