I really liked the first Dead Space. I somehow missed the announcement of the second one until a few months after it came out; a buddy was asking if I'd played it and I said yes, then he proceeded to tell me all about DS2 and I was like WTF are you talking about? I was shocked when I found out the second one wasn't available for PC.
Yes, turning off vsync helped my mouse. Still not perfect though, it seemed like there was way too much animation in the characters legs and torso. For example, you would run one direction and then try and run back and the character would make a bit slow moving deal of stopping, catching his balance (sorta) and turning, then running again. I found it annoying.