It is very sad that although the OS community has made very good games in fields of FPS, MMORPG and turn-based strategic games, the results in the RTS are not comparable to the rest.
I look at AoK and its expansion as the best game ever in its kind because the it's, you know, perfect in its kind. It's circular, every civ has its flaws and strongholds. To this day it's THE game of my lan partys and a single play can take up to 5 hours. I enjoy others RTS, and I love the story behind some of them, but when it comes to multiplayer, then Age of Empires II rocks and it's the way to go.
I've tried some free (as in Freedom) RTS but they are just not finished, with not enough manpower and without a very strong idea behind them. (also they tend to be futuristic whereas I think this is just a possible scenario and also our past is free to use, no royalty in greek and roman civilizations .-P)
I REALLY would like to have the expertise to enhance this situation... But I just don't have the skills and the time to learn them, I hope I could become a good beta-tester for this things. In the meanwhile I can just hope a change in this situation and that a least somehow one day the Pandora could run a AoE game. Or some engines running AoE graphics like happened to something else.