It's revolutionary and it's an awesome, timeless blast fest.
The whole point of The Ultimate Doom is the adrenaline rush. The game takes place in huge levels which could easily take you 10 minutes to beat but there is often more to them than meets the eye, such as innumerable secrets where you can find such elusive treasures as the chainsaw or a multitude of powerups, armor upgrades and powerful weapons like the BFG. Ugly (but beautiful) monsters swarm the area, and will give chase if you piss yourself and run (not likely hopefully). The games enemies range from small fodder like grunts to gigantic cyberdemons spoiled with a rocket launcher that could wipe you off the face of hell.
There are 3 chapters in the game including an extra chapter made for The Ultimate Doom. The chapters usually have about 7 levels plus one or two additional secret levels that require some serious investigating. If you die at all in the level all your progress is wiped and you once again start off as a lowly marine with nothing but a pistol and 50 bullets. You might want to save during the level at times when you have plenty of health, or you'll just take it like a real man and accept fate. But you'll still want to save to make sure you don't start at the beginning of the WHOLE GAME when you launch it again. At the time this game would have has plenty of eye candy, although as you probably guessed this isn't the case now, although modifications exist to tune up the graphics to display 3D effects. Corridors and rooms are rendered in full 3D but the enemies and your weapon are all sprites. Pixelated, but your unlikely to get a headache if your running it on a modern machine (look into the Doom collectors edition). At the time the original was released these graphics were the latest in technology so don't go disrespecting them.
The sound effects are gratitious but the music score is far from epic. On most levels the music is little more than a 20 second loop, it's done so it sounds like a rock band but it's all midi. It fits the theme but some people think it was a missed opportunity. The sound effects are pretty good though, the enemy grunts are well done and the guns sound pretty cool.
If there is any FPS I would want to take to the ends of hell it would be Doom, so whats yours. The Ultimate Doom is an updated version and it's available in a collectors edition that is compatible with Windows XP. It even comes with Doom 2, and the infamous Final Doom. It's not a bad purchase, Doom still has kickass gameplay, you'd do well to give it a shot.