Who cares if theres nothing new, this is how I like Doom!
First off I would like to talk about the game in general. Even though Final Doom brings nothing new in terms of gameplay, enemies or weapons you still get that satisfying action because, in my opinion, Doom and Doom 2 are perfect games. You will notice that the level size has expanded- even though most levels in the game are around the same size as the levels in Doom 2, some levels are huge like Mount Pain and more. Overall TNT and Plutonia will take you longer to complete than any other Doom game because the levels also feel more complex which is good if you like a challenge.
Speaking of challenges, Final Doom is also a lot harder than Ultimate Doom or Doom 2 because many of the enemies featured later in the other Doom games and you will find more weapons earlier. Unfortunately, because there are a lot more enmies at one time, you'll die often because of the lack of ammo and the amount of foes. So it will take several attempts to complete a level sometimes, even on the easy difficulty modes.
I think the main problem is that the game just doesn't feel as well designed as the other Doom games- some levels arent that good though most are great. But I still think Final Doom is excellent because I just can't get enough of Doom and the gameplays not changed- it's the way I like it!
The main reason I rate it very high is because it's a real challenge and you get 2 Doom stories and a total of 64 levels- you just don't get bored!