With 3D Realms going bust and subsequently finding themselves in court against publishers Take Two due to Duke Nukem Forever living up to its name; the people at Wired have written an article detailing what went wrong with the developers at 3D.
By the end of 1999, after blowing several publicly proclaimed release dates, Duke Nukem Forever was nowhere near completion. Half the weapons were still just sketches, and when a new version of the Unreal engine was announced — one designed for live, multiplayer online battles — once again Broussard opted to upgrade.
The full article can be read on their website.