I find it hard for any strategy game ever created to be better or more special than AOC. AOC came out to be the perfect game, and the things that made it so good may not be intentional by ES. From what I remember they were playtesting AOK with 75 pop limit.
AOC had the battle mess. Hundreds of units fighting without slowdowns without lag and that was because of 2D. Also 2d never gets old, cause pictures never get old. Look at other classics of the same game era, Red Alert2, Diablo2, Worms, all time classic 2d games.
Should I be able to make 80 Trebuchets in a black forest crazy Death match game and block the passages? no
Should I be able to build 150 Fully Upgraded longbowmans to see all the screen full of arrows trying to kill an elephant? No...
Should I be able to take 25 Villagers and build 3 castles on enemys base? No...
So much flexibility but still balanced gameplay.
The only disadvantages AOC had was the slow gameplay in the standard Random Map gametype and the lack of further patches by ES.
I am not saying that AOE3 isn't going to be good. I hope it will be, but (seeing the demo) I find it almost impossible to be better from what AOC was in its time.