Question: what is the difference between ultimate doom and final doom?
Answer: Ultimate doom- Doom 1. Original Doom had 3 episodes (27 levels), ultimate doom added a 4th. Final Doom- Think of it as standalone DLC for Doom 2 in a way (although it actually provides twice as much content as doom 2 itself does). It provides 64 levels using doom 2 assets such as monsters and weapons.