The source for the physics engine (https://github.com/TTimo/doom3.gpl/tree/master/neo/game/phys...) looks rather interesting. Might contain valuable additions for other physics engines to pick up.
Also, and this is subjective I suppose, I don't remember Doom 3 doing anything that 'felt' or looked better than even what the contemporaneous engines did (such as the version of Havok used in Half-Life 2).
So I guess, there probably aren't valuable additions, but I imagine there is much to tinker with.
From looking at the game code, I see odd things like rolling barrels animating their rotation as though the physics engine itself doesn't handle rolling contact.