I didn't expect very much from Doom 3 to be honest but my opinions were totally changed by the time I finished it. Gameplay wise there was nothing original at all, but at being a great piece of entertainment / theatre, Doom 3 achieved just that. I loved it, pitch black room 22" monitor, surround sound on / 5.1 headphones it was excellent!
Doom 3 multiplayer sucked more than a sucky thing that sucks a lot, elephant and mud springs to mind.
..but that aside what a fantastic engine as a platform for other material.