Pardon the shortness of this entry, I'm using a keyboard with a broken space bar, it's tiring to type too much right now.
So a lot of people are really hating on this-- and I honestly can't figure out why. The game is great fun, it has a sense of humor, it's well paced, has good variety... it's certainly no game of the decade, but it's still hella better than games such as the CoD/MoH/BF series as far as single player goes.
The driving sections which I normally despise, are short enough with enough breaks in them to stay acceptable, the shrink ray sections I wish were more frequent (not necessarily longer, but in more places) but they're still excellently done and played with quite well, the normal FPS gameplay is superbly done, etc etc etc. The only real problem I had with it was the alien hive, which was just... too dark. Not metaphorically dark (no, that art fits in quite well), but literally too dark, too... colorless. Sure the Nevada desert areas are a bit drab, but at least they have an old west appeal going for them, and they aren't quite as monochrome and visually dark and... well, boring. The casino/duke's hotel was excellent, and I enjoyed the water battles at the end as well.
The weapons are nicely varied, with only the M1911A1 being taken from the real world (though the shotgun is at least feasibly an RL shotgun), the sounds are excellently composed, and the storyline works as well as any Duke storyline has, which is to say, it's an excuse to kick ass. Hearing duke actually pissed of (and not just dryly saying he's pissed off like normal) was an excellent touch for this duke nukem fan.
All in all... I've spent ~50 bucks on far worse than this. Certainly I have no regrets, unlike my purchases of BFBC2 and CoD:BO.