In 1993, Doom was a big hit. It changed the face of RPGs, with its amazing true 3d walls, landscape, etc.
1994 saw the release of Doom II. Everyone expected a lot, and I bought it the day it was reported to be out in my area. Unfortunately I was disappointed. The graphics were brown and dull, and there was not much of a storyline. All you know is that you have to save Earth, nothing more. "So this story doesn't make sense, okay.", I thought, but I was still going to enjoy shooting those monsters. Unfortunately the levels were much more dull than Doom 1, and there were no major changes to weapons or enemies. Only the introduction of the Super Shotgun and about 3 more monsters.
I hope I don't feel this way about "Doom III" which is coming out fairly soon.
If you haven't got Doom 1, I recommend it over Doom II. It is more futuristic, more entertaining and there are better levels in general.