I'm experiencing the same problem, and as others have stated, it makes the game quite literally unplayable.

Now ideally I'd like an option to disable acceleration all together like others have stated, but I read about how that's going to take some time. That being said, this isn't just a case of acceleration being annoying, some sort of bug is clearly causing it to function in the reverse of how it should, and considering the fact that others have been able to play without experiencing this, I'm thinking maybe fixing this bug will be a quicker fix than coding in a setting to disable acceleration? At least that's what I'd hope, since I'd like to be able to play a bit over the holidays.

Now what I did notice is that if I plugged in an Xbox 360 controller, the aiming was fine. However, the game isn't fully functional with a controller; some functions are inaccessible and movement becomes awkward because the game has clearly been designed specifically for a keyboard and mouse, so mechanics like strafing which are pretty integral to the controller experience aren't very fluid.

I don't mind that the game isn't optimal on a controller because I prefer the keyboard and mouse anyway, but unfortunately the keyboard and mouse are unusable at the moment.