Well, as I said earlier, you can check their forums. EB has the main ones here, and RTR in TWCenter.

I can't think of much that RTR adds beside what you said:new skins, new map, new factions... However there are plenty of mini-mods and mods for RTR, like the 4TPY (4 turn per year) mini mod.

EB adds a lot of new features:practically too many to list here. 4TPY, 4 stages of Roman Reforms, Olympic games, the Roman Cursus Honorum, different government systems, voices in the native language, new music, extensive information of both troops and buildings... And plenty more. If you want the full list, go to the EB homepage, and look under "Features". Also, I recommend you check their previews of both May, June and July. Plenty of goodies to drool over... You can find them in their forums.