I was out of town this weekend, so I had the chance to download the demo but not to play it at any great length.
They've definitely upped the Duke attitude factor from the original Duke 3D. That's one of the first things I noticed. To a certain extent, it's almost a parody of itself, it's been so enhanced. I'll be curious to get the full game and play through it.
As for the gameplay mechanics, it's not going to blow you away. The controls felt a bit loose to me, but that could just take a little getting used to.
It's probably not going to live up to other recent games in the graphics department. One noticeable distraction is that there's considerable texture draw-in. You'll come up on a rock or a sign that will intially be a colorless mass, then it's "oh, hey. there are textures."
The usual compliment of weapons are present: in the demo you had the chance to use the Devastator, shrink ray, rocket launch, shotgun, pipe bombs, pistol and a rail gun.
I recall moments from Duke 3D where you're left puzzled as to where to go next on the map. I still got some of that feeling as well, but again, it could just be that I'm still getting used to the overall gameplay.
Still excited for the game on the 14th, that's for sure.