Dead Space, EA's 2008 game of weed-whacking in space, is really good, but the PC version is a little wonky, specifically with regard to the mouse control. Disabling vsync and futzing around with the sensitivity can dramatically improve things, but out of the box it often suffers mouse lag, weird sensitivity, and other issues that can make it feel anywhere from "off" to nigh-unplayable. Keep that in mind when you snag it from Origin, where it is currently yours for the taking, for free.
Developed by the sadly now defunct Visceral Games, Dead Space tells the tale of Isaac Clarke, a heavy-handed sci-fi reference and engineer aboard the USG Ishimura, a massive "Planet Cracker" spaceship that falls foul of the Marker, a mysterious relic of Unitology—basically the Scientology of the future.
Trouble is that the Marker actually has power: It turns people into ravenous, hideously-deformed zombie-type creatures called Necromorphs, which of course doesn't keep the brainiacs in charge from bringing the thing aboard the sealed environment of the ship.
Things go predictably sideways, and it falls to ol' IC—who by the way is also suffering from hallucinations and appears to be in the midst of a total psychological breakdown—to clean things up, with nothing more at his disposal than a futuristic Black and Decker set.
It sounds silly, but it really is good stuff —and you can't beat the price right now. As with all of Origin's 'On the House' offerings, it will be free until it's not (it will eventually go back to $20 but EA doesn't say when On the House freebies expire) and if you grab it during the giveaway, it's your to keep forever.