Not as bad as the Haters say; Not as Good as the Fanboys say; More Stable than the original.
The only significant change in gameplay from the original G3 is the combat system. While nearly everything is still the same, the role of "Endurance" ( or lack there of ) is increased. Once you have run out of "Endurance", you may not strike your opponent. Originally in G3 you merely could not do any significant damage, however you could consistently "StunLock" your opponent against a wall, or other obstacle, and kill him with a thousand paper-cuts. This has been ~fixed~, and yet combat against multiple enemies is now very awkward; After dispatching one opponent, you must now flee to regain your endurance, and then return to the fray.
Simply put, if you were a die-hard fanboy of the original G3, you will endure the issues and be enthusiastic about the expansion. If you were a die-hard hater of the original, walk on by. If like me you are a fan of the entire Gothic Series, and want a last chance to be the nameless hero for several hours, this will do just fine.
It is criminal that Jowood released this product as is, but they are actively patching it. It is also criminal to be charging full price for such an incomplete product. So if you aren't a fanboy, I recommend you wait it out. The price will drop like a hot stone very quickly, and the responsible parties may have a chance to fix the majority of issues.