a bit disappointing since doom 3 was an improvement on the formula
Doom 3 was a good game in its own right, having excellent graphics and art style and captured the horror elements of the original quite well but the shooting stuff was pitifully boring. As a user previously mentioned, encounters basically resumed to teleportation and monster closets. Both were frequent in the originals but that is really all Doom 3 did. In the originals you have enemies attacking you in diverse combinations and from diverse angles, which always kept things fresh.
From what I've heard from attendees, Doom 4 will retain the atmosphere of Doom 3 but will greatly expand it, meaning that there will also be vast, open spaces along cramped corridors. It will also have a great emphasis on mobility, double jumping and dodging enemy projectiles. This will be an old school game with AAA quality made by the best of the best, meaning there will be no regeneration, no weapon limit, over-the-top violence (seriously), no aiming-down-sights, no reloading...Exactly what Doom fans want.