DNF has been in development hell for the past 12 years, and has become the poster boy of vapourware, and the gaming world's longest running jokes (for example, linking the games initials with the status of a race car that fails to complete a race). 3D Realms has long stated (rather petulantly, I thought) its release date as "when it's done". Aside from some screenshots in the early days, the only news was a trailer released in late 2007 (which was also the topic of the first post in this blog).
Part of the problem has been the chopping and changing of technology midstream. Starting with the Quake II engine, 3D Realms switched to the Unreal engine in 1998, a newer version of the Unreal engine in 1999, Unreal 2.0 in 2001. The physics engine changed from Karma to Meqon. There was a very public spat between 3D Realms and their publisher, Take Two, and repeated no-shows at various tradeshows.
Is this necessarily a bad thing? With its long development cycle, DNF would have to have been something awesome, otherwise it would have been one of the most pilloried video games in history (though maybe not as much as Daikatana...). Duke Nukem 3D is widely considered a landmark game in the FPS genre, and much was expected of its successor, especially from its early screenshots. It's entirely possible that the game would have been released to poor reviews, which would have spelt the death knell of 3DR anyway.
But it could have been a good game, too. It looks like we'll never know.
Update: The 3D Realms website is back up, only to say goodbye (complete with staff photo).