I've been meaning to play through Ultimate on UV, but I still haven't beaten E4 on HMP. Still need to beat Doom II and TNT on UV as well.
Plutonia, Plutonia II, Alien Vendetta, and Hell Revealed II are tough as hell, I'm not skilled enough to get past map03 on any of those.
Check out Doom the Way id Did and Knee-Deep in ZDoom, those are forgetin' awesome.