Id Software 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," Hollenshead told GameSpot.
"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."
Despite the early stages though - id "really just started on that last year" and is still hiring - Hollenshead is confident that Doom fans will be excited by the direction.
"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.
In the meantime, Hollenshead said to expect another Wolfenstein showing at E3, and "I expect that we'll have some new stuff at E3 that we haven't announced yet."
Id is also currently working on Rage and Quake Live. Rage will not be out this year, Hollenshead said, but the technology is now complete.