More missions, more units, more fun.
Well, there are 4 extra campaigns, 4 additional civilisations (each uses the same tileset), 5 new units (some of them, like Slinger and Camel Rider are rather useless, while Scythe Chariot is a very good unit) some new technologies and maps.
Ensemble Studios also added some tweaks to the gameplay, for example double-clicking on unit selects all visible units of the same type and pressing F11 will show you how many soldiers do you have and how many you can train.
Unfortunately, I could copy "the bad" section from my Age of Empires
review without doing any changes, because there are still some flaws from original AoE: you can still have problems with commanding your army, and there are bad proportions of units. Ensemble Studios fixed these problems in Age of Empires 2
The Bottom Line
If you liked Age of Empires, you will probably like Rise of Rome, too. You will get some new missions, and you'll appreciate those little tweaks in interface. If you are unsure, download a trial version - there are 3 missions unavailable in full version.