I was pleasantly surprised to be adding this to my list of favourite RPG's. ...I liked it better than almost any I've played, and I'm a big player of RPG's. It may be a little old, but still very good.
There is a lot of depth to the game. There are many, many, many sidequests, with a lot of variety, so they don't get too stale or repetitive (and really, who doesn't want to track down a pot dealer or lead a bunch of pirates for a while?). There is still a fair bit of the standard kill-these-people-and-come-back style questing, but I didn't get bored with it. Actions taken in game have consequences (I got a prostitute killed. ...Oops). There are three different major factions you can join as well, so there is some room for replay from a different perspective. I downloaded this game, then promptly spent the next several weeks glued to my computer. I have also infected my husband, who is playing it now.
The early levels can be extremely challenging if you haven't read up on tips on how to spend your experience. I made some poor decisions off the start and felt like I wasn't accomplishing much until around level nine. ...But once you get the hang of making yourself capable and start getting new equipment, things progress fairly quickly. The difficulty was definitely much easier towards the end of the game (though not without challenge still, which was nice). All the way along, they tend to include some things in the world that are SUPPOSED to be difficult or impossible to kill at that point, but they generally also warn you to about them in game. ...Sort of a refreshing idea, that the puny beginning adventurer can't easily slaughter everything he encounters.
I haven't played the other games in the Gothic series, but got the strong impression that there would be some added benefit to trying Gothic I before this one, as they reference it often. It's definitely not required, though. That said, I will definitely be checking them out now that I've finished Gothic II.