The Age of Empires series is a history based real-time strategy game. The player is able to complete the campaign or compete against the games AI which can be set to various difficulties, however in Age of Empires online, there is a plot twist, the campaign consists of various quests. Which can be completed in Coop mode or single player and if you feel the urge to play against another player it is possible to PvP.
I have been playing AOEO for almost a week now completing anywhere between 2 to 5 quests a day and I must comment that the game play is quite good so far. The graphics are not as ground breaking as in Age of Empires 3, which for the record was quite good in the year it was released, although considering this game is free, who I am I to complain?
Upon completing each quest you will receive XP to level up and gold and depending on each individual quest you may receive loot as a reward as well. It is possible like I said earlier to PvP in a 1 v1 or 2v2 AFAIK.
Currently there are two available civilizations, the Greeks and the Egyptians with more in development, we are most likely to see them later as the game heads down for release.
AOEO is still in BETA but it is possible to sign up as a BETA tester, here.
To conclude, I personally have high hopes for Age of Empires Online