I played the demo earlier today. I was initially impressed by the intro and some of the humour, but it descended very quickly into juvenile idiocy. What really killed it for me was the "trying too hard" attitude - Duke 3D had a lot of the crassness and innuendo, but it was never 100% at the forefront. Forever is doing its best to copy the original, failing, and then amplifying that failure by about ten times. Sorry, Gearbox, drawing cocks on whiteboards is not what Duke Nukem is about.
The actual gameplay itself is a mixed bag. I didn't have the mouse issues some people claim to have, and the actual controls were pretty fluid and responsive for me. Visuals were detailed, but way too bland and surprisingly dark for my liking, despite clearly trying to emulate Duke 3D once again. The "two weapons at once" thing feels like a pointless contrivance designed for the sake of modern trend-hopping (along with the vehicle section and regenerating health), and the perhaps most damningly, level design lacks much of the openness of the original that made it so replayable - instead of secrets around every corner and multiple approaches to every level, you've got a bunch of "cinematic" moments, scripted boss fights, button-mashing and short, linear levels. At least there are gadgets, but their use will probably be extremely limited, hand-holdy, and only required in extremely specific circumstances, rather than them being optional augments to fit into the player's unique style.
I have to wonder if the demo itself is just bad, especially considering that it's so short that I was genuinely surprised. I'm used to short demos, but seriously, I don't think I played this thing for 20 minutes before it was over, and that's including the intro movies and fiddling with the options menu (I also died once because I got stuck on level geometry).
Overall it's not terrible, doesn't necessarily indicate the final game will be a complete train-wreck, and some of the run-and-gun enjoyment of Duke 3D is there, it's just buried under layers of modern trends and piss-coloured graphics. I am genuinely puzzled why there is so much scripting, so many cutscenes, the two weapons at once thing etc. going on - are they trying to make a throwback game with fast and fun gameplay? Are they making a more realistic and modern shooter? It feels like some weird amalgamation of the two and it just doesn't work, and almost makes me think it's the result of executive meddling at the hands of someone who struggles to breathe, bitching because it doesn't have iron sights, vehicles or a turret section, because Call of Duty has them and it sells X million copies. That, or Gearbox just does not understand why Duke 3D is so fondly remembered - whatever they might think, it's not just because of the attitude.
Even though I think the game has some potential, I'd still steer well clear of it and stick with Serious Sam.