"It's going great. It's awesome," id's design director Matt Hooper told Eurogamer.

"We have so many talented people, and as a company we've grown so much. But we've been able to keep them [the Doom 4 and Rage development teams] separate.

"With Rage we're concentrating on making our game as good as it can be. Those guys support us in whatever way they can. And we'll do the same for them."

Doom 4, due out simultaneously on PC, PlayStation 3 and Xbox 360, was expected to show up at last year's QuakeCon. Explaining its no-show, id CEO Todd Hollenshead said the development team was not ready to demo the game. It is still without a release window.

Doom 4 is, according to comments made by Hollenshead in 2009, "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, and if I told you why, I would get my ass kicked when I got back. So I'll just have to leave it at that.

"It's very much deep in development. But everything I've seen on it is classic Doom, so I don't really have worries that people aren't going to like it and start talking about it," he said.

"They're [the Doom 4 team] going in their own direction," Hooper added. "They're doing something Doom fans will be happy with.