If they do it right it might be a good game, but that's a big if. No Strogg shit please.
- Go for a true oldschool approach with game design. Quake is a very direct game, so keep it direct and make no compromises. Throw out collectibles, modifiers and all that shit, you don't need it. If your game is good people won't care about that. If they do they are not your target audience anyway.
- If the level design of Doom is of any indication then the guys at id are capable of making excellent things. However, first and foremost they need to ditch that focus on arenas, embrace the old school of level design once and for all and go for what made Doom and Quake levels so great: making dungeon-like levels as opposed to a chain of arenas, the kind of dungeons you'd find in an RPG. They need to dive head first into this mindset or they won't be able to succeed where Romero, McGee and Petersen succeeded. Traps, moving geometry, teleporters galore, emphasis on verticality, useful secrets, well thought-out weapon and item progression, ambushes and good flow that's not interrupted by story or arenas after arenas. Exploration and combat must not be separated like modern shooters do and must go hand in hand.
- Keep the Lovecraft aesthetics and the moody atmosphere. Doom is a very flashy game with its mostly heavy metal soundtrack while Quake is a darker game with an emphasis on eldritch and otherworldly locales. The great thing Quake managed to do however was tie this and its frantic gameplay together instead of trying to scare you like Doom 3 does while reducing the pacing of the game to a crawl. Keep it fast but keep it moody as well.
- Which brings me to: get rid of the glory kills and the health and pickup mechanics entirely, and revert back to the classic style. Glory kills are goofy but aren't that much out of place in Doom; I mean you could punch monsters to death or hack them with a chainsaw. In Quake, however, they'd look beyond silly. Quake is a violent, gory game but I cannot picture Ranger sticking his hands in a shambler's mouth and ripping its tongue out. Reverting back to the old health and pickup mechanics would compliment the oldschool dungeon level design instead of undermining it like Doom 4 does, would force players to keep an eye on resources and manage them accordingly and would encourage players to explore the level and maybe find secrets. Doom and Quake never force you to explore levels but they encourage you to do it regardless. This and the emphasis on arenas are what make Doom 4 merely a pretty good game instead of the great game it could've been.
- Make monsters great again! I'm semi-joking here, but the Quake bestiary, despite being quite small compared to Doom 2's, works very well as a team overall. There is still monster infighting, which is great, but good use of monster combinations can kill a player quite quickly. Doom 4 didn't explore this so it looks like the monsters are all working solo instead of trying to kill you 'together', if you get what I mean. Ogres rain down grenades on your hidey-hole while Fiends try to catch you and efficiently eviscerate you when you are cornered. The fully 3D level design possibilities and the synergies between monsters in Quake can result in a myriad of situations that weren't possible with Doom 1, 2 and 64, and that I wish I'd see with Doom 4.
- The multiplayer must be as fast as QW/CPMA with no loadout crap and with proper item placement.
EDIT: modified a passage because it was contradictory.