Just played the demo myself and I must say I don't see why some people are moaning.
Graphics are not that important, you can distinguish who's Duke and who's the enemy. If graphics mattered to people, games like Terraria, Minecraft and Bioschock 2 would not have sold that well

.
First level was fantastic, second level sorta sucked as it felt a bit empty but I'm sure there will be a few levels in the full version that make up for it.
People tend to forget that 3dRealms worked for over A DECADE on this game, from what Gearbox have been saying they spent hundreds of hours just getting the game stable. I, along with many others, knew this game would never live up to the hype.
As for having 2 weapons only, many other successful games use it and I didn't find it detrimental to my enjoyment of the demo.
I'm sure Gearbox was fully aware of the piece of dirt they'd been handed from 3DRealms and that unless the game was put out asap it would spell the end of Duke Nukem. After Forever I'm sure a much better Duke game will be coming out.
Still betting on Duke and can't wait to play the full version.