All the different available versions of DOOM confuse me (DOOM, DOOM II, Ultimate DOOM, Final DOOM, Which ones do people recommend?
Doom is the original game developed by id Software.
Doom II is the followup released about a year later. The look and feel is the same, but the maps are all new and the game has a new weapon (double barrel shotgun) and some new creatures.
Ultimate Doom is a redo of Doom that includes a new episode and the Doom II double barrel. I can't recall if it had the additional Doom II creatures. Beuller? Anyone? Beuller?
Final Doom is actually a pair of megawads of Doom II(The Plutonia Experiment and TNT: Evilution...consider them mods although they run as standalone games) that were created by a couple of teams of Doom fans using the editing tools of the time. id scarfed them up and released them as an official product. Both megawads are considered tougher than either of the original games.
My preference is Final Doom, probably because I only got it a couple of years ago and it's still fairly fresh. Recommendation? All of them. If you really pressured me, Doom II or Final Doom.