It's mostly the same demo that's been shown around since early this year (which was an updated version of the demo from last September).
Visually, I think the game looks very good. At least on the PC. Except for the 'depth of field', which is badly done. Unfortunately, the post-processing effects are grouped into one setting.
The demo didn't give much to do. It was only parts of the levels, not the full levels that will be in the game. I think they will be grouped into chapters. If you dig around in the files on the PC, you can find interesting stuff (and some spoilers).
I did have fun with it, but I don't think it's very indicative of the final build or much of the game in general. There's a ton of stuff that hasn't been seen and there is cool stuff that's been talked about in recent previews.
Beer and the HoloDuke (in the back of the blue truck) are in the demo. The HoloDuke is much more effective now. Has some pretty funny one-liners too.
Also, cheats work. In game, type "dnclip" for noclipping (you can get to the penthouse, the area after you beat the Cycloid.
It's below the stadium and takes more than 5 minutes to get there.
), also "dnweapons" to spawn all the weapons from the game. Old School.