The package you get for 20 bucks is quite good. Doom 3, plus the extensions, companied by Ultimate Doom and Doom II gives really a lot of hours for your money. The multyplayer is dead but the singleplayer experience is all you need.

This game includes:
Doom 3 with some gameplay changes:
- More healthkits and ammo
- Flashlight has been removed as a seperate weapon and replaced with a shoulder mounted light
- Surround sound is now compatible with most soundcards rather than being exlusive to Creative EAX
- Ammo counter stays in the hud even for weapons that have their own ammo counter
- 16:9 screen ratio means zomed in view and removal of the ingame zoom
- Game is a lot brighter than the original Doom 3

Doom 3 Resurrection of Evil:
- Same changes as above
- Removal of arcade machines

Doom 3 Lost Levels:
- Cut down areas and levels from Doom 3
- Prototype area layouts (that actually made into Doom 3) have been put back into Lost Levels
- Last part of the last level is how Doom 3 should have been

Ultimate Doom:
- Medkit red cross has been changed to a pill with one half red and the other half white
- Nightmare is easier with normal speed imp fireballs and Pinky run speed
- The WAD file is compatible with Doom source ports, giving you limitless gameplay with mods
- Resolution is set higher, making targets distinguishable from far away but is locket to 30 frames
- I have the feeling that the game is easier than the original classic Doom

Doom 2 + No Rest for the Living:
- Same changes as Ultimate Doom
- No reference to Nazis and no Nazi soldiers

I pitty the fact that we are missing Final Doom and Master Levels for Doom. Overall the package is worth buying.