Doom 3 BFG edition re-releases Doom 3 with all its expansions (Resurrection of Evil and the Lost Mission) and includes both the original Doom and Doom 2.The graphics for Doom 3 have been improved quite a lot, with character textures greatly improved and all skins rendered in much sharper and more crisp detail. The colours have also been made more vibrant, giving the game a better look without diminishing the tense atmosphere, the contrast between light and dark has been upped adding to the tension when entering a low light situation. The graphics for Doom and Doom 2 haven't been changes as, lets be fair, it would have ruined them.
The gameplay has been modified slightly for ease, my favourite new addition being that the flashlight can be used whilst holding a weapon (which it couldn't before). The sound is as awesome as ever, with no apparent changes. A big problem with the game though is loading and saving take long times and the saving screen will sometimes pop up at annoying times.
Multiplayer modes have been added to all three games, I'm afraid I haven't actually tried any of them yet, but they sound amazing nevertheless.
In the end this is a great pack with Doom 3 in the best shape its ever been in and the original games thrown in for good measure.