Gothic 3 seems to get more and more unplayable the better your system is.
First played it on a 6800GT, 1gb RAM, when it first came out (without community patches). It was rather slow and buggy, but still playable.
Next, 7950GT 512mb, 2gb RAM... started to get really slow, like a slideshow in some parts, the FPS just hit rock bottom.
Now, 8800GT.... completely unplayable. Just so, so laggy. I've put the game back on the shelf, and I don't expect to play it again unless the community patch team work miracles.
By the way, if your computer does run it ok (and it is a kind of lottery whether it does or not) Gothic 3 is a rather good game. There are choices throughout, mostly on who you decide to side with, but some of the quests do have alternate paths. The gameworld itself is very well designed, great art direction, and the soundtrack is nice too. There's lots to do and there's a big game world to explore, ranging from desert, to forests, to snowy mountains.
The only weak points, for me, were the combat and the performance. But even the combat is forgiveable once you get high level, because you can kill pretty much everything in one or two hits. Until you reach that, however, expect to die a lot from stunlock and bugs.