You will be greatly rewarded for spending time with this game!
At first I was a bit put off. I noticed a lot of things that annoyed me after being used to polished Oblivion. Like the unrealistic way other characters react when hitting them hard, the silly grunts your enemies let out when you hurt them, bleeding undead skeletons or the permanent lens-flare from a sun shining even through mountains. Being able to slice up a huge troll with ease, while being ripped to pieces by a boar, who made my character stunned and unable to fight back, particularly made me feel disappointed.
But, from then on, the game just gets better and better, you are greatly rewarded for ignoring the first few issues on the surface. It seems to never stop pouring new amazing content at you. The game just drags you in, and soon you will be wandering around the beautifully rendered woods realizing how life-like the nature surrounding you is. The atmosphere is magic, and exploring the world is a true joy because of its amazing diversity. The graphics is by far the best I have seen in any role playing game, perhaps with the exception of Oblivion, it is just so full of life and it's astonishing to see such a huge world being filled with such varied landscapes, with varying themes like desert, grasslands and of course the great winter plains of the north. It is all accompanied by some really fantastic music, that sets the mood spot on. On my computer the framerate is surprisingly smooth, even on the highest settings (I have an overclocked Geforce 7900, dual core CPU, 2GB RAM). It runs much smoother than Oblivion.
Both the main quests and side quests are varied and interesting. There's literally hundreds of quests, and the characters involved all have their own unique voice as you communicate with them, which helps immerse you into the story. The amount of speech put into the game is mind boggling, must be countless of hours of dialogs in there. However, after a while you do find some repeating patterns in the quests. It's basically fetch that thing, or kill that beast or enemy, in various wrappings. But, the way you have to accomplish this varies a lot, and even better, you usually have lots of different options on how you want to solve a quest based on you or your character's strengths. For example, you could steal an item, help the owner so he will give it to you or just use brute force to relieve him of it.
Building your character is an interesting process, and you have a lot of options leading to a very unique personality and gameplay experience. Unlike in many other RPGs you do not get the benefits from leveling up automatically. You receive experience points which you need to spend by finding the right teacher or magical shrine. You also need money to get the new benefits. So, you need to put more work into developing your character than normal, but it is also quite rewarding once you get through this. The various abilities are quite demanding on experience points, which means you have to play a really long time before you get close to reaching your characters full potential, which is good as it leaves something new to be discovered for long time.
I have not yet completed the game, as I enjoy playing all the small side quests. But, I imagine it has a lot of replay value. The game has several outcomes, and you are left with many choices that will decide the fate of the world. Basically you need to decide whether you want to take sides with the Orcs or humans. But, by playing smart, you can get the most benefits form both fractions, without taking any side before things gets really serious.
There's a lot of talk about which game is better, Oblivion or Gothic 3. At first I thought Oblivion, now I think Gothic 3. But, it does not really matter, if you enjoy this genre, you owe it to yourself to play both. And finally, please do patch this game to the latest version before you play! It makes a big difference, and is hardly an optional thing to do. The game has technical issues in its original form, however in the age of Internet where we get patches delivered so easily, I see no point in whining about it. The latest patch fixes most problems, and you should ignore any review basing the score on the problems that are now already fixed.