This game is outstanding. Why? Atmosphere is the key. The music is really good and matches the regions (there are three, Myrtana, Varant and the North Lands). Furthermore each city has it's own look and feel, additionally to some landmarks which also have their own theme. By the way, you can basically go anywhere you want. There's also no real order in which city you do quests. Some regions are shut off, but "only" by guards - which you can either fight or do quests for, or simply take another route. By the way, if you like the game, check out on Vimeo "Nur ein Spiel" - it's a great documentary featuring among else Gothic 3 (only in german, but worth watching).
Since there are so many reviews, here a rumour: It is said that you can import cities from the old SimCity by renaming the save file from .cty to .sc2 That said, who has the old SimCity? Well.. it's source code has been released. It's available under the name "Micropolis" on SourceForge!
This game is a piece of art. It truly delivers the feeling of being on the edge of the universe, the far outlandish Gemini Sector - and offers all the freedom you'd expect in this situation. Heck, even the restrictions feel right. It's just great!
My reasons why you *need* to play this game: -outstanding story -great graphics (for that time) -awesome setting -best. game manual. ever. Really. If you haven't played this yet, do it - it's like a blend of RPG, adventure and flight sim.