People named the obvious things, but from doomwiki[0] I noted those:

    > * Flashlight-projected character shadows are disabled.
    > * More light sources in the levels.

The latter may make the game a bit prettier, but the first one was one of the few things that made Doom III stand apart, and might be a letdown.

http://doomwiki.org/wiki/Doom_3:_BFG_Edition#Differences_wit...