From Histroy to Myth!
AOE was based aroud history but AOM is more or less just pure Myth.
Gameplay is pretty much the same but the graphics have been improved.
In AOM new aspects have been put in such as the Mythical beasts that can be used to fight with and the new story lines.
AOM is a great RTS game with aspects better then AOE2 but then agen people will not leave AOE for this game. So if you intend to buy this game i would say play AOE first.