The "Quick"look on Giant Bomb is a nice overview over some of the levels for people who want to see more than the demo. http://www.giantbomb.com/quick-look-duke-nukem-forever/17-43...

For those who don't have the 50min to watch it. Both of the guys commentating don't like the game at all. It's supposed to be boring and archaic, and then there's the lazy humor...