Fun and flawed liked its predecessors, but not as good this time.
It diverges from 1 & 2 mainly in the way the plot is structured. Basically, there is none. Your ship lands, you start fighting Orcs, and now you're on your own. The objective is to either destroy the Orc oppression and free humanity, crush the human rebellion and enslave humanity, or side with Xardas and portal away. There is no story progression per se. Your only barrier to entry is reputation, which you build by helping one faction or another. Once you have enough rep with a certain group you can speak to one of its leaders and do bigger quests which earn you bigger amounts of rep. Once you get up enough rep to talk to the head honcho of a faction, you do the final set of quests and the game is finished.
The major failing of Gothic 3 is that it's too open when it comes to the 'story'. Since there is no planned storyline with specific events, you end up doing the same kinds of quests over and over, centered around liberating towns or ratting out rebels. Fetch X number of weapon bundles, kill this guy in this town, collect fire chalices, etc. The gameplay becomes quite repetitive liberating town after town, doing nearly identical quests for each, and regardless of faction, all of which ask you to do the same kinds of things.
Even the main characters, Gorn, Diego, Lester, etc., have no direction of their own and very little to say or contribute. For the most part, they're there to help out in combat, and no longer play a role in the story, such as it is.
The environments can look incredible when the settings are tweaked, putting out draw distances as far as your hardware can handle. The gameworld in terms of virtual square mileage is much larger than those of Oblivion and Gothic 2. Character models are another story. The Orcs look ok (though not nearly as well-designed as those in Gothic 1 & 2 - why they changed them, I don't know), but the humans all look like cartoon characters with tiny heads and blocks for arms and legs. The other monsters are all nicely designed and modeled.
The gameworld has plenty of places to explore - caves, mountaintop ruins, waterfalls, lots of towns and buildings, and so on. Exploration is the most enjoyable part of Gothic 3, which is the trademark of the Gothic series. The downside is that you can't swim underwater like you could in 1 & 2, only on the surface.
Combat is unbalanced and not very well implemented. Enemies can only attack one at a time and some monsters can knock you back or down with a high frequency, causing what is referred to as stun-lock. Whenever I was knocked down by a wolf or boar, 80% of the time it would end in death as my character would be unable to recover from their rapid knockdown attacks. Patching has helped a bit, but it still persists. Some weapons are badly overpowered, like the high-strength 2-handed Orc weapons that do enough damage to kill multiple enemies in one swing. Magic is a bit out of whack too - fireballs and such hit 100% of the time unless it hits another creature or obstacle in its path first, usually making running or dodging futile. NPCs using slower 2-handed weapons tend to be at a disadvantage because they either miss when their opponent jumps back or they're hit with a rapid succession of strikes from which they are unable to recover. Friendly NPCs often hit each other accidentally in combat, usually leading them to attack each other afterwards, something that's only funny the first few times. Armor doesn't protect very well in proportion to its cost. I went most of the game without any armor at all, bypassing everything else and saving to buy the Paladin armor instead. There are other difficulties with combat, but it's workable. That's all you can say for it.
The voice acting sucks, but it's Gothic, so what do you expect.
Gothic 3, despite its many flaws, was fun. Of course, this is after tons of patching. I wouldn't have played it in its initial release state. They've got the exploration part, but they're missing the story and characters, and that's why it's half the game Gothic 2 was.