Further news surrounding Doom 4, is that the game will not be entitled Doom 4, but instead, that will be in the subtitle. This is due to the fact that Doom 4 will not be a continuation of the Doom 3 storyline - which has a few of us feeling a little bewildered. Surely a continuation of the Doom 3 storyline would be a remake of Doom 2? Nothing yet is set in concrete, so no judgements can be passed yet.
Why did they decide to make this move? Part of the reason is that the fourth Doom game will not be a continuation of the storyline for Doom III, according to Willits. Doom III was basically a "reimagining" of the first Doom game's storyline (a la the revamped Battlestar Galactica). So willl the fourth Doom game be a continuation of, say, Doom II's Earth invasion? Willits wasn't giving up any story ideas yet.
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http://news.bigdownload.com/2008/08/01/quakecon-2008-doom-iv-wont-actually-be-called-doom-iv/Stolen from OMG! PC Games.