Although I enjoyed it there is not much replayability for me.
Let us have a look at the first 3d iteration of Duke Nukem:
It started with a very linear part: You fall down a linear vent from the roof. But that's it with the linearity.
Right after that you can decide to either go to the crates to get to the hidden living room, or to the ledge with the secret RPG, you could junp outta the flat to get behind that enemy in the burning container or walk the street.
And with the RPG you can either enter the cinema through the front door, or through the backdoor leading to two comepletely different approaches. And I am not even gonna start on what you can do when in the hall of the cinema and the multiple paths from basically anywhere.
That's one aspect of what made DN3D so great for me in terms of gameplay.
Yes, I sound like an advertiser ... but if you look at the concepts they have for Duke Nukem 3D Reloaded I am much more looking forward to that one.
Just one example:
http://dukenukemreloaded.com/mp01-outside.jpg (There are more sheets with the interior parts)
Yes, they change the original Hollywood Holocaust layout and expand on it. Purists will hate that ... but then we get an editor and people can remake the original HH without being a paintball arena.
Still it is Hollywood Holocaust with all the exploring and multiple paths and the key elements of the original. Oh, yes, keycards will be replaced with more creative puzzles.
That's why I became such a huge fan of the project.
And my personal opinion is that one reason Gearbox gave the license to that project is because that game contains the stuff a lot people miss from DNF: All weapons, non-linearity and mod-tools.