This is a solid game undermined by a terrible launch, but with many problems fixed is now worth trying out.
Age of Empires Online had a now-infamous launch, replete with numerous bugs, a limited set of features at launch, and a pricing scheme that quickly resulted in it being labeled as severely over-priced.
As of the most recent patch and the release on Steam, most of those problems have been fixed. Bugs are relatively few, the game now has most of the features it should have had at launch, and the pricing is now very reasonable, not to mention that it has a free to play mode.
The game plays as a relatively straightforward real-time strategy with individual missions against the AI, but outside of that has a persistent layer, where the player unlocks units, upgrades, and equipment over time. There is also a player-versus-player mode that does not rely on player progression.
Gameplay:
The action is standard RTS action, where the player builds up a base and units over time and attempts to defeat the enemy forces and destroy the enemy bases. Like other RTSs, the game has campaigns with numerous missions, including some that focus on base-building and others that focus on controlling forces. Some quests are quite innovative, but many more are repetitive.
At present, three civilizations are readily available for free-to-play players, with a fourth only available for those who pay to unlock it. The civilizations do play somewhat differently, although not as distinctively as, say, the different factions in Starcraft 2. Balance is reasonably good, though not as tight as for other RTS titles.
The persistent game is not tremendously compelling, but does add another interesting layer. The player unlocks units and upgrades by accumulating experience through playing missions; individual units can be improved by adding equipment to them, which equipment is dropped through in-game missions, and which can be crafted from materials found in the missions. The overall system has similarities to the armory system in the campaign for Starcraft 2.
Player-versus-player does not use the persistent system, and instead offers all units and effectively all upgrades to the players.
Graphics, Controls, Sound:
The cartoony style of the graphics has been controversial, but it is attractively rendered, and makes following battles very straightforward, as units and effects are easy to pick out. Style-wise, it is either love it or hate it and not much in between, but functionally, it works. Controls are typical as for RTSs, but not as feature-rich as they could be, and feel just a bit unresponsive; they are about on par with Warcraft 3, but well short of the highly responsive controls of Starcraft 2. The sound is well-done and appropriate to the theme, if a bit repetitive at times.
Problems:
Setting aside problems in the game at launch that have since been fixed, the two main problems are repetitiveness and player-vs-player. While there is an end-game, generally focused on collecting better equipment for your forces and vanity buildings for your capital city, the end-game missions get repetitive fast. Some more variety in missions is badly needed.
Player-versus-player, while decent, is nowhere near the Starcraft 2 industry standard. The pacing is slower, balance is not perfect, not many strategies are viable, but worst of all, there just aren't many PvP opponents available. PvP is there, but may continue to be a sideshow to the real game, which is the PvE missions and the persistent progression.