Body hopping, breaking the fourth wall, high stakes player immersion, diverse gameplay, and a whole lot of rule bending! Omikron is the first game I remember where expoloiting the rules was actually part of the game. One of the only games ever where dying in-game can actually advance the story. Omikron not only has an exclusive David Bowie soundtrack, but he also voices one of the key characters you can meet and interact with! I will say this game had a couple technical issues I hated. I won't get into them, because, hey, if you think about it right, they may even add to the experience for you, but they're why I dropped a star. Otherwise this game is one of those rare gems that will give you something completely original and blow your mind.
Very fun in and of itself. With gameplay that differs quite a bit from the first two in the series, it was a little difficult to get into this at first, but once I did, the more open concept was a welcome addition. After doing absolutely everything there was to be done in the game like three times, I can say that I still wanted more. And really, I don't think I can say that about many games. I did however think it was a little broken to not refer even once to what must have been the aftermath of the metal age of Karras. No steambots or even spare parts lying around. To get my fill of that sort of thing, I had to go play the fan made expansions through http://www.thief-thecircle.com/ (I may have even made one or two inferior levels myself). I highly recommend the t2x project.