Doom is just one of those games. It's probably one of the most well designed and intrinsically fun games I've ever played. It has perfect balance and excellent pacing. The enemy design is impeccable with great weapons to murder them with. It has a fundamental understanding of the combat dance you have to do when you play these ganes and why that's endlessly enjoyable. I'm not sure if every level is to my taste, but I can't think of a really awful one either. It's just perfect. Just skip episode 4 though, it's not worth your time.