If you enjoy Duke's style in humour then the humour in this certainly will not disappoint you as it's very much like Duke Nukem 3D's ; but obviously it's not for everyone. Honestly I don't really understand why some critics call Duke's humour unfunny but yet praise humour in games that is mediocre at best. As for critics that question Dukes character; I really hope they are joking. I can accept various opinions on Duke Nukem Games but to question the protagonist that makes the franchise so unique and enjoyable definitely raises questions as Duke Nukem is a gaming icon that still has an appeal;even today and is a nice change from the typical serious heroes you see in a lot of recent games.
Oh and don't worry about all the controversy this game has sparked off for all it's mature content; we all knew it was bound to do that if it was going to be a follow up to Duke Nukem 3D which was also quite controversial at the time. If the game was watered down to appease some critics; it just wouldn't be a Duke Nukem game would it?
The game is not without it's flaws but it has interesting elements and very interactive environments. The enemies and bosses are pretty cool and challenging.The only things I don't really like about this game is the linearity in levels, a checkpoint system, only carrying two weapons, strength tests and the new Health system. This game will not have the replay value of Duke Nukem 3D but really what game does these days? Aren't all shooting games nowadays pretty much linear? It's a trend this game regretfully followed but luckily it has things that make it worth checking out.
Now that Gearbox owns the rights to Duke Nukem; I imagine things will go a lot smoother in later games as 3D realms was biting of more than they could chew trying to keep up with the times as they just didn't have the numbers or resources to pull it off while Gearbox is a much bigger company which has been something the Duke franchise has been in need of. It's a safe bet Duke will have more adventures to come; always bet on Duke ;)