After reading about loading times, I'm installing it to the hardrive before I even play it!
I Think you need to have played and enjoyed the originals to appreciate its awesomeness. If you don't then you just won't "get it" tbh.
We have been spoilt with fancy fps's for years now, its nice to have a game thats stuck to its roots and i'm really enjoying it so far.
I really think people are just disappointed because they expected the wrong thing.
Its not about being a next gen shooter its about taking you back to the old skool days of duke nukem which I think it does really well. If you wanted a next gen non linear shooter then you were always going to be disappointed, they're old hat now themselves its nice to have something thats different from what is now the norm.
I bought it wanting a game to take me back to my childhood memories of duke nukem 3d and this game does a sterling job of it for me, i'm really enjoying it.