Dentrassi - I'd like to make a couple clarifications -- Technically speaking, the games you listed are still built on the Doom3 engine. Megatexture is an addition to the D3/Q4 codebase. Also, saying that ETQW's tech is developed primarily by Splash Damage isn't entirely correct. They're doing the game development, but AFAIK the bulk of core engine development is still Carmack and crew.
I'd agree that Doom 3 and Quake 4 were mediocre, but I don't think the problem was the engine. On technical basis alone, I still think they're beautiful and impressive games. I just wish the gameplay had been... ummm, at all innovative or creative. C'est la vie.