I really liked some elements of Doom 3, especially the Soul Cube and the cooperative fighting with the sentry bots.
What I really hated about it was that it felt like they'd finished and polished the game, then gone "shit, we need to make it longer!" and added loads of pointless backtracking with wall panels popping off behind you to reveal imps. I'd love the original version with the padding cut instead of a version with extra levels.