I really should think before I post.
Some of my Doom 4 demands:
• Large, expansive, non-linear environments, like in the old games. Doom 3 was painfully linear, with most doors and areas being conveniently locked or blocked off.
• ACTUAL futuristic weapons, not just normal weapons that look "future-y" or generic pew-pew weapons that shoot bright orbs.
• Massive destructibility. I'm not saying every FPS needs to be like the Red Faction series, but static geometry is outdated. Players should be able to affect the environment in a number of ways.
• Better monster designs. Doom 3 had decent, detailed, nicely animated creatures, but they didn't strike the kind of fear in me that the originals did. I'd like to see some really sick designs, ala H. R. Giger. And obviously, no more of the gimmicky spawning, it often made the fight less challenging since you could just crown them with the shotgun while they were materializing.
• Less scripting. Give the player the option to make their own decisions, which will have drastic effects on the progression of the game.
• At least some environments based on classic Doom 2 maps, like Suburbs, Downtown, Industrial Zone, The Living End, Tricks and Traps, Nirvana, Monster Condo, etc.
• More emphasis on the demonic elements of the old games. It doesn't have to be straight up Satanic, but occultist and demonic imagery/symbolism has always been a big part of the Doom games.