Nice game but too short and with little new features.
New features (compared to previous AoE games) are mostly the necessity of setting. Most importantly, those are the natives whom you can befriend to gain their very interesting and unique units and the Home City which can ship resources, units and upgrade as you gain XP by doing almost anything in the game.
The game should have been much better graphically. Strangely, I find Age of Mythology visually more appealing. It seems that graphics in Age of Empires 3 looks sharp only with maximum zoom, which is useless for normal gameplay, while it tends to become blurred when you zoom out.
The sound is good with some nice voice acting and cutscenes.
The only great disappointment in the game is length of the campaign which I finished in about 3 days of playing. It spans from the first days of colonization to the days of wild west and has quite good story, but it is really too short.