I still have the problem... I thought it was alright, and that I didn't aim straight because I was tired that night.
When I continued from the bank just a few minutes ago, I noticed that the problem was still there. When making slow motions with the mouse, it feels pretty much like the cursor in the menu. It's not as noticeable when moving fast, but it's still a problem.
YESSS. This is terrible. I got kind of excited about this game because I never played it back then. I wanted to but for whatever reason I didn't. Now I try to get into it and it's just impossible. I cannot play with the weird mouse movement. If I try to move smoothly left or right, it will dip and turn up or down on it's own. It's impossible to focus for a headshot because of this. And headshots make the game much easier.
I had to give up because of this. It was making me sick.
Googled as best I could and can't find a solution. Heck I can barely find relevant information about this game outside of reviews. Messed with my mouse settings and the game's ini settings and nothing helps enough.
I also found the music to be too loud. Had to turn it off. Couldn't hear voice or sound effects over it :|