From what I've heard in interviews with different developers over the years, 3D Realms kept wanting to do more and more with it. They truly wanted to innovate the genre (and make fun of the genre at the same time) as best as they could. We kept seeing new tech, new concepts, etc.. so you could imagine it would be hard to "innovate" as you watch other other developers and tech jump ahead of you. Basically, they had no direction and by the time Gearbox got their hands on it (and pushed it out the door) it was just a collection of loosely tied together bits of unrelated gameplay.
Duke's downfall was the development time. If the team had just set a goal and gone for it, regardless of what the industry was doing, we could've had a great game.
*It doesn't help that Randy Pitchford made the game sound like the second coming of Christ :/








