One of the best RTS games out there. A must-own.
In this game, you pick between 13-15 civilizations, each with unique technology and units, this game also helps in education on history as you pick between the missions (Attila the Hun, Barbarossa, El Cid, etc.), you can even review about the different weapons, units, etc. in the History icon in the main menu. There are also plenty of game modes to choose from, if you get bored in story modes, try playing the Single Player mode, where it's just pure build and destroy, no stories.
I recommend this game to RTS gamers who still haven't played it yet.