Rome and Medieval II were pretty weak without mods.
But Rome with Europa Barbarorum mod is probably one of my favorite games ever.
The amount of complexity I got used to in those mods disallows me from going back and playing vanilla total war games.
I'm playing Medieval II with Stainless Steal mod, its ok, better than vanilla, but no where near the complexity and historical accuracy EB had.
I liked the Vanilla versions (although they were pretty easy), Barbarian Invasion expansion for R:TW was a bit harder and very enjoyable though.
Never played the EB mod (I assume that was for the expansion?) but played the Rome:Total Realism mod to death (Seleucids FTW!) and was liking how the Warhammer mod was looking (don't know if they finished it though).
@Bill, never played any of the Total War games in MP, for me they were like Civ games, something intrinsically SP, much beard scratching and philostopising, the MP, as it was single battles and micro management without the pause button never really interested me that much.