I remember when I first heard about S.T.A.L.K.E.R:Shadow of Chernobyl. Especially after I saw the movie that inspired the game (http://www.imdb.com/title/tt0079944/). I was giddy with anticipation like DNF. I followed the development but kept getting disappointed because they kept delaying as new engines came out and they rewrote the game to use those engines. At some point you have to say, OK choose a branch and run it out and stop making changes. Ultimately, this is what THQ did and they did produce an amazing game. I think 3DRealms could have learned a lesson from them. My number one rule of engineering: "You are never done, you just run out of time and/or money to make changes."
Too bad, when DN-3D came out it was my favorite replacing Doom II, but at least they both live on in the community. The Duke will always be around FOREVER!!!