IMO this game is much better with Total Realism, but I suggest that you play normal campaigns first.
Oh, and TWO expansions? Which is other one? I only know Barbarian Invasion.
BI is harder and better IMO, it is just pure awesomeness when your heavily fortified city (good walls and full garrison) is attacked by Horde at night. You kill and kill and kill them, but there is allways more. Firearrows piercing night sky (and hunn flesh, bwahahaa! ), struggle at walls, gates are broken down and last stand at city core, which ends to heroic victory and retreating of barbarians. Western Roman Empire stands still!
Once my city was attacked by 3 hordes (first came huns ((that fight above)) then those vandals, and last one I don't remember. My superior troops won every fight, but in the end I had only two battered units in city (can't remember which it was anymore) and then riot started Lost the city after all.
Nothing beats when playing as Western Roman Empire at hardest difficulty level. You're going to be screwed
Btw, is there any "Tolkien mods" to Rome Total War, like was for Medieval Total War? I haven't played RTW since last winter, so I don