Ask AdamH, and he'll tell you Ep4 on nightmare is about the second hardest Doom movie after whole Doom2 on nightmare. There's a list of all the authors of Ep 4 maps somewhere, let's see if I can't dig it out...
Ah, after some Googling, here we go:
E4M1 : HELL BENEATH by American McGee
E4M2 : PERFECT HATRED by John Romero
E4M3 : SEVER THE WICKED by Shawn Green
E4M4 : UNRULY EVIL by American McGee
E4M5 : THEY WILL REPENT by Tim Willits/Theresa Chasar
E4M6 : AGAINST THEE WICKEDLY by John Romero
E4M7 : AND HELL FOLLOWED by John Anderson
E4M8 : UNTO THE CRUEL by Shawn Green
E4M9 : FEAR by Tim Willits
So now you know.
BTW, John, bet you didn't think E4M2 could be finished in 16 seconds when you made it
. I like that run...