http://www.ageofempiresonline.com/

I've been a huge fan of the AoE series from the beginning, but this doesn't sound good to me. Maybe it's just me, because I don't like online games in general. Aside from that, where's the history and why only one civilization? Your thoughts?

I think the idea is to be a quick pick up and play game. Age of empires has always been quite an involved game that I often found if you didn't finish your opponent off quickly, the map could take many hours. Not ideal for an online game really.  I would also imagine they will expand it over time, see it as an opportunity to charge more money.
For me Age of empires 2 with all the add-on packs was the best you could get. I felt 3 really never came close to being as good.