ID themselves said from the _very_ beginning that they never intended Doom3 for multiplayer.
They said you can do it, but it'll suck. They learned with Quake2 that single player and multiplayer games are 2 entirely different things. It takes a lot of tweaking and performance tradeoffs to get the best performance in either case.
And for Doom3's defense. I liked it, I don't know why people were so dissapointed with it.
I built my family a gaming rig for my father day's present. (It's unfortunate that I almost never to get a chance to play on it.

)
I bought three FPS games for them; Doom3, Farcry, and eventually Halflife2. Nobody touches anything but Doom3, except for my youngest brother who plays counterstrike source online. They played the other games a bit but Doom3 was the one that anybody actually put time into to beating.
Of course HL2 got overshadowed in a LARGE way for "Rome: Total War". One weekend I came over and sat down and beat HL, and I don't realy understand what the hooplah was about.
Keep in mind that Doom3 was designed for more then just your seasoned FPS fan, its designed for people that may haven't touched FPS for a few years.
Quake4 is going to be the multiplayer version.