The problem I have with it is that it offers nothing new, and critisizes games that have offered new gameplay mechanics. It's not the worst game ever, but it should have been a lot better. It's predictable, childish, Dukes voice is just annoying, and the humour, as everyone says is redundant. It's like the developers attended a conference on level design, then left after 10 minutes to get back to work. Ohh, a hole in the roof for enemies to jump down. Ohh, enemies teleport behind me. Ohh, enemies open locked doors at set intervals. There's nothing dynamic about DNF at all.
If you think back to DukeNukem3D, the things I liked about that game were it's dynamics, pulling levers to squash enemies, setting traps, that sort of thing. But there's very little of that.
People who want a new and improved DN games should look elsewhere, like Serious Sam. If people want a laugh, then Fallout3/NV is hilarious if you play it right. There are simply much better options out there for the things that made Duke special.