The idea of your online representative being the capital city is a great one, and well integrated with fellow players: you can visit a chum's city in an instant to buy special items and partake in friend-only quests. Knowing people will be looking at your layout is as strong an impetus as there will ever be for arranging shops and storehouses in neat lines that spell out LOL.
The other aspects of your capital city include an absolutely bog-standard crafting system and an assortment of places to buy things. Crafting is limited to two specialities (unless you're not paying to play, in which case there's one) and works in tandem with buildings that produce raw materials.
In an unwelcome lift from FarmVille and its ilk, the production cycles depend on your checking in to store items and restart the process. The lack of storage space is a pain: you're all too often having to re-arrange the suitcase and toss stuff out, and you get even fewer storehouses if you're a dirty freeloader.
You can certainly play Age of Empires Online without handing over any money, but the very best free-to-play games value their non-paying communities because their sheer mass and commitment support the top five per cent who pay for the thing. Age of Empires Online does not. In the long term, it's crippled for free players: no ranked player-versus-player, certain units unavailable, a stunted tech tree, limited crafting and limited storage. If you have no plans to spend money, look elsewhere, because AOE Online does not do the business model justice.
In fact, for paying players, it's even worse: £15 for each civilization (at the moment, Greek and Egyptian; the Greeks come in the £20 boxed version) or a whopping £80 for the season pass, which grants you all content released in a six-month period. If you want the new civilizations down the line, cough up. To play this game long-term will cost much, much more than its competition.
That said, if you just want to toe-dip in Age of Empires Online for free, it doesn't feel too trammelled. Playing against others online is still possible and you can acquire basic upgrades.
Those crafted items really make a difference in matches, especially against the same civilization. It's incredibly disheartening to get into a game and realise all your Greek opponent's spearmen are simply better than yours because they have a purple spear of doom that you can't craft for 10 levels and the health pants of plenty. It's surprising to see balance given such short shrift in a game that surely aspires to competitive play.
There are other things that need fixing. The pathfinding is terrible and will sometimes cost you the game. And one more thing for which there is no excuse: AOE Online not only requires Games for Windows Live (a service Microsoft should be ashamed of rather than promote) but a constant connection. Fair enough, but if your broadband flickers, the game automatically quits out to the title screen. It doesn't give your connection a few seconds' grace, or save any progress, it just quits, mid-mission. It's an insult to players to make a game that requires a constant online connection but has no way of dealing with a temporary dropout. Solutions exist, and they're not rocket science; StarCraft II, for example, gives a 60-second countdown for the connection to re-establish.
It breaks my heart to give Age of Empires Online a less than brilliant score. If you'd told my teenage self that, one day, AOE would have this much content and you could play it online against actual people for free, my spotty head would have exploded. It's as good as mechanically identical to previous entries in the series, and although its new structure spreads it a little thin, there's still a fine strategy game underneath it all. But the context has changed.
Age of Empires, great as it was, doesn't quite stand up against the best in the RTS genre today - and Age of Empires Online doesn't improve on its mighty predecessors in any meaningful way in-game, while adding a lot of bumf around it of questionable value. It's still a grand name, of course, and in some ways a grand game - one trumpeted as 'Microsoft's triumphant return to the RTS genre!' So let's put it this way: it's certainly a return.