Imperium Romanum isn't much at all LIKE Tropico, so it is hard to compare it. Tropico was less a city builder and more a society builder, which is why it was so brillant. You, as the ruler, were a character in Tropico, something that is missing in Imperium Romanum (and most every city builder). Pity, Roman era would have been great to have a build-your-own governor style game.
I played the demo, and almost bought the full version. For some reason though, I feel it is lacking something. I hate to sound like RH, but you can literally bargain bin dive and grab Glory of the Roman Empire and have much the same game (minus the slightly improved graphics engine). Scenarios aside, the game is (according to the reviewers) almost identical.
"Neca eos omnes. Deus suos agnoscet!"
(Kill them all. God will know his own.)
-- Arnaud-Armaury, the Albigensian Crusade