Gothic 3 ain't that bad
Well since then it has had several patches (1.6 is the latest) which apparently has improved things considerably. Now lets clarify, this is still a system hog of a game engine. I have a top of line rig (e6600 C2D, 8800 GTX and 3 GB of RAM) and this game still can chug along at times especially when in towns. That being said, the game's graphics are very nice. The textures are better than Oblivion's (although recent mods such as Qarl's Textures Mod improves this) and the beauty and the lighting of the landscape is very nice and subtle and has a little more personality than Oblivion IMO. The character models and animation are serviceable at best.
The role-playing is pretty good, there is lots of things to do. Create armor and weapons, brew potions, you can follow the path of a swordsman, warrior, archer, mage or thief. Better yet you can combine those skills and develop your character how you want without being stuck in a particular caste. There are lots of quests and different factions with different goals and you ally yourself with these factions and play out the game whether to help the Orcs and enslave your own people or help the Rebels defeat the Orcs. The role-playing does have some issues, this isn't deep RP that you will find in the NWN series, but it does give you some options on how you can play the game. I think the RP in Gothic 3 is superior to that found in Oblivion.
Combat is tricky, it can be very frustrating and you may find the difficulty setting of medium to be a little too difficult (others have stated this). I've found it to be just about right. The land is crawling with alot of creatures anyway, so when you do get in a fight, I prefer it to be challenging. If you your really not that into the combat part of the game, the easy setting makes the fighting a snap.
The size of the world is immense, it is open and sprawling and is probably, if I had to guess, three or four times larger than Oblivion. Just exploring the world is fun and there are tons of herbs and plants. On that note, alchemy is much simpler than Oblivion. The potions are fewer but are much more useful. I never got into alchemy in Oblivion because it really wasn't necessary. You can also do some smithing and create armor and weapons, again its pretty straight forward, get some training from a smith, buy or find a weapon/armor schematic, find the materials, then go to the smith shop and create the item. And that item will also be worth something because the economy is very well balanced. Good armor and weapons are very expensive and is hard to find. So it makes smithing very worth while part of the game-play.
On a side note and this may not be very important to some, but its an added bonus, this game has one of the best musical scores I have ever heard in a game. It is also appropriate, when you go into a deep dark cave it naturally transitions into something more ominous. I haven't gotten tired of listening to it.
Well, that's it for now. I am only about 14 hours into the game, with probably at least another 100 hours to go.