To summarize, I don't have a strong opinion on the Doom 3 engine either way. I'm just pointing out that based on
what I've seen, the engine might be kind of limited in application. In contrast to earlier id engines, Doom 3 seems to move a lot farther away from "general use" towards specialization.
For instance, would it be a good idea to try to make Quake 4 based on the Doom 3 engine? Even if it's released half a year later those lighting effects will really bog down the competitive FPS. I seem to remember Carmack saying that for a multiplayer online FPS, the Quake 3 engine was all anyone would ever need. In a way that seems to be saying that in fact the Doom 3 engine is
not designed to be used in such a game-- at least not without some modification?
I'm not saying id is going to go out of business, or even that they'll lose licensees over this. It's just in the past with Quake 2 vs Unreal, Quake 3 vs UT, (and other engines on the market, like Lithtech), all supported essentially the same features set. Now with Doom 3 and Unreal 2k3 we're seeing vast differences for the first time. And, depending on what the developer is trying to accomplish Doom 3 could either be a godsend, or completely unusable.
Maybe at this point it's too early to really judge...I'm just playing the Devil's Advocate.