I got ahold of the game early, and I can say that it's almost identical to the demo.
There are no graphical improvements since the demo, and very few of the bugs are fixed (I was driving and actually slammed into the air at one point, then I backed up and suddenly a bridge support appeared that hadn't been there before). The good thing is, there are slightly less framerate issues, though it still does drop at times. The draw distance is still frightfully bad, and there is virtually no environment/object damage memory (drive back to an area 30 seconds later and it's like you were never there). The graphics are rather bland, and the textures are underwhelming, the lighting is only medicore except on select objects/surfaces.
Now for the good, the gameplay is just... fun. Shooting/running over peds is a blast, blowing cars up is fun. In the full game there are larger vehicles, such as 18-wheelers and big bulldozers, that make it much easier and more fun to maul and blow up other vehicles. Some of the side missions are fun, some suck. The main missions are generally interesting, if not sometimes monotonous.
Overall I'd give the game a 7.8-8.0, the glitches are too noticable and even hindering at times to give it more, but definitely worth picking up.