I dunno. I know a lot of people who thought D3 was very UNlike the original DOOM (I and II) because the original DOOM was all very simple graphics with no interactions other than pickup key and run into doors.
In DOOM3 the environments were factors better and more interesting, and there were people to talk to, the sound files and video clips, searching for the combinations to things and solving the puzzles. Plus, you didn't have to cruise around endless totally-featureless rooms for a key.
It's almost to the point where you can't compare D3 to the original DOOM on anything other than the constant shooting factor.