I'm more excited about having the engine available than I am about Doom 3. As mentioned above, even recent games like Call of Duty are still using the Quake 3 engine to great effect, and the Doom 3 engine will likely be longer-lived than it is. If more games end up looking like Doom 3 (in terms of quality, not style), I'll certainly be happy. Real-time lighting, shading, and detailed physics all add quite a lot to the visuals of a game, and in turn add to your immersion and enjoyment.
But, of course, I'm not too worried about release dates and delays. I've got a job and friends that occupy plenty of my time already, and lots of other enjoyable things to do. It'll come out when it's ready (which is better than before it's ready), and I'll have a new toy to play with in my spare time, nothing more.