While we've yet to see any previews of Doom 4, during his keynote speech at Quakecon yesterday, John Carmack did let on just how dedicated id Software is to developing the game. Evidently, id has closed down its mobile games division, who past titles have included Wolfenstein RPG and Rage HD, so that they can focus on Doom 4. In fact, following the release of Doom 3: BFG Edition, all of id will focus on Doom 4.
Hopefully this doesn't mean that progress on Doom 4 is falling behind, but who's to say? When asked for the status of Doom 4, Carmack said only, "It will be done when it's done."
To date, there's essentially nothing to go on concerning a story, release date, gameplay, or anything really. This past March, a few alleged Doom 4 screenshots were leaked. However, id has neither confirmed or denied the images as either real or fake, Rage's design director Matt Hooper saying only that the images "have nothing to do with what you're gonna see in Doom 4...When we officially show things you'll see awesome."
As for the story? Again, nothing's been confirmed, but id co-owner and CEO Todd Hollenshead has said that Doom 4 is, "not a sequel to Doom 3, but it's not a reboot either. Doom 3 was sort of a reboot. It's a little bit different than those." He's also suggested that Doom 4 will take place on Earth, and will feature more run n' gun gameplay of past Doom games.
It was reported in 2009 that the British writer Graham Joyce had been hired to develop the storyline.
If you need a Doom fix to tide you over for now, the original Doom is now on XBLA, and Doom 3: BFG Edition will be out in the fall.