The game starts skipping as soon as the gameplay begins (after the intro). The framerate stays smooth, it's something that happens to the character. When I try to, for example, look around, the whole screen goes nuts, it starts acting as if mouse was borked. The same thing happens with the input from the keyboard, the character moves too far away or too close, his animation skips, he flickers and other strange things happen.
I'm on Win 7 64, Athlon 64 X2, 4 gigs of ram and Radeon 4870.
Any ideas?

i have the same problem. drives me nuts. there must be a solution!?!

i changed mine to run in win xp sp3, and admin rights.... seemed to work for me!!!. thanks!
ah crap, its now doing it again.....its insant death trying to time jumps..or falling from heights. damn it all...

The game can't cope with multicore-processors.
Try assigning only one CPU to the game in the Task Manager's Processes tab.
It's more of a workaround though, Windows does not remember to keep the CPU settings so you have to change these every time starting up the game (and Alt-Tab out).

Actually, you can make Windows use only one core. All you need to do is to create a new shortcut and add a few parameters. E.g.
C:\Windows\System32\cmd.exe /C START "<Name>" /high /affinity 1 "<Path>"
The shortcut set to the above target will run the command prompt and load the provided path file using only the first core of the processor. <Name> is just a name for the app, it's the path that's important. Here is a completed example:
C:\Windows\System32\cmd.exe /C START "Tomb Raider" /high /affinity 1 "C:\Games\Tomb Raider - Legend\trl.exe"
Sometimes there may be permissions issues if you need to run the app as an administrator. If this happens then you add a directory parameter ( /d <directory> ) into the shortcut. The above example would become:
C:\Windows\System32\cmd.exe /C START "Tomb Raider" /d "C:\Games\Tomb Raider - Legend" /high /affinity 1 "C:\Games\Tomb Raider - Legend\trl.exe"
And finally, you can change the icon from the command prompt icon by altering the properties of the shortcut.

Using RunFirst is probably the easiest way to set affinity since it does it only for the game and automagically.
It's also a free program . . . =)

Thank you very very much. Played the game, bought it today, and it runs like...
well... like hell, I turned of the 2nd Core (via taskmanager), but with RunFirst, this problem is solved :D

Bringing up an old post here, but I've got the same problem. Actual framerate is 100% smooth, but the extra jerky mouse makes it seem like the video is stuttering.

Also, moving the mouse makes your character animations faster, thus making your character actually move faster.

Here's a video demonstrating this.
I'm exaggerating the mouse movements in the video, to get the effect to really show.

System specs:
- Windows 7 64bit.
- 8GB RAM
- AMD Phenom II X4 965, overclocked to 3.9GHz.
Mouse: Logitech G400.

Few months back, I also tried everything to fix it. Installing mouse drivers, running game under OpenGL, setting core affinity manually or with RunFirst, etc... Nothing works.