I always hated running around, finding key cards and secret walls. Most of the time I really couldn't care less about getting to the next level. I just want to frag, frag, frag! So I guess singleplayer is basically lost on me. I usually play it just to say I've played it. Although I did enjoy the half-life singleplayer.
All I really care about is that when doom 3 comes out, all the players who used to play quake, doom, etc, will come online, and there will be more people for me to frag!
dfi