Should Final DOOM ever be released on XBOX Live Arcade, I believe they should add more than the normal 12 achievements since Final DOOM IS 64 levels total. Make achievements for TNT and Plutonia, maybe a couple level-specific achievements, say for example:
Plutonia Map 11 (the maze with nothing but Arch-viles and a super shotgun) - Kill 10 Arch-viles with the Super Shotgun without dying on HMP or higher. (HMP has 12, UV and Nightmare have 18.)
Go 4 It - Complete all 4 secret levels.
Fan-fraggin-tastic! - Kill 5 or more enemies with one BFG shot.
Old School - Kill the Cyberdemon using only the Rocket Launcher.
Property Damage - Kill an enemy with an explosive barrel.
BUZZKILL - Kill a Cacodemon with the chainsaw without it hurting you.
Maybe a couple funny ones:
OVERKILL - Complete a level with 101% kills or more.
CIVIL WAR - Allow at least 2 enemies to kill each other.
UNDEAD - Kill 5 enemies resurrected by the Arch-vile.
I say the game deserves at least 50 achievements to make up for 64 levels and all the crazy ish that DOOM brings.