Anyone blaming Gearbox is an idiot, among those responsible for it not meeting expectations can be blamed on the following people and factors:
1. 3D Realms. Yeah Gearbox bought the franchise, but it was to get rid of what was becoming a tired industry joke. and they know it as Randy Pitchford even said he doesn't care about how well the game scores.
2. The Fans: When developers start listening to fans and giving them what they want, of course it's going to suck. Fans wanted the game, and therefore were expecting that since it was in development since 1999 , and the fact that it had been delayed again and again, it would be a manifestation of the best game ever made. and with that hype is hearby created and it spreads like an unwanted itch, and it increases people expectations. It's like the problem with Bioshock 2, where devs thought it would be good to play as one of the popular aspects of the first game and in this case it was the Big daddys. And that game sucked a massive pancake poop. the second game that is. Bioshock is a great game before people make gross assumptions.
3. Modern Shooters: Everyone is so obsessed with realism it's not even funny anymore. anything thats beyond the laws of realism is considered bad. the only solace anyone would have would be games like Serious Sam and Duke Nukem, but unfortunately the latter became influenced by Modern Shooter Trends adding the "OMG SO REALISTIC HE'S HOLDING ONLY 2 GUNS" to the gameplay.
4. Since there havent been any other games of Duke Nukem that have been released during DNF's dev hell, DNF havent had any chance of being able to bring in scores of new fans to follow it. the only people and this has been mentioned in many reviews that will enjoy DNF will be the people who played DN3D.
I digress, people including gamers will have to learn to accept that not everything will be what we expect when it comes out. anyway, what happened to the olden days when everything was fun? oh wait, the internet.