In Dead Space, VSync is enabled by default, which prevents some really nasty visual tearing but adds about a half a second of lag into mouse movements. This can be compensated for by adjusting mouse sensitivity, so make sure you tweak your control settings for an optimal experience. Might be worth turning that off. Also, you can throw things at no cost and you dont have to fight every monster if you can avoid them.

Can we say, offline messages Steam?

First comment. :O