its not that, its not the engine.
its the media that makes the game. Id and Raven both were able to farm out thousands of man hours for modeling, animation. If I had the money, if I was doing this and had hit the lottery, this being a hobby.. to do that type of thing, it'd be done. Hiring people, instructing them of the stuff needed, micromanaging how all of it can be integrated; then it'd be fat.
knowing then what i know now, wfa, hell q3 would be different. i don't think i'd have jumped ship from wfa's path, but stupid bugs that i know about that we went through before are just soooo simple. little changes here and there could've been done. but see everyone is under pressure to get things done at a certain time. I have a luxury that others cannot afford; i can play. i have no real timeline, just get it done. I build the exe, someone comes up with some new math for sometihng, i can play with it for a few weeks. It's design at the purist level.
right now the game works, its 99% done (except for some "aesthetic" ents). if everyone just took it and played it, made docs, fired up servers, the "little" bugs that crash things would be squashed quickly and it'd reach a stable, distributable stage before you'd realize it. seriously maybe 3-4 hours tops to find bugs, then maybe 4x that to recode, retest, sign off on them as fixed. right now i'm hammering down flare effects still on the client side purely, instead of server-side ents. sorta like q3test flares that the renderer only sees and it doesn't matter if they are in the server-side bsp ent list or not.
but back to the topic, could we make a doom3? yea, that i have no doubts of. could i create all the media that goes into it? nope.