Age of Empires Online MMORTS is out (and it's not all bad, apparently), let's start talking about how you can pay for it, shall we? Of course, the game is free to download, and you get the game's two empires to play with right away. But developer Gas Powered Games are working on releasing new content all the time, of course, and Microsoft has announced at Gamescom that those really interested in the game will be able to pick up a "Season Pass" that will grant access to all premium content currently available. That pass will cost $99.99, and last for the first six months of the game.
At this point, we only know about a few different content packs, and there's a deal for a free Defense of Crete Booster Pack when you buy both Premium Civs, so everything on the market right now will set you back only about $60. But keep in mind that the Season Pass lasts until February of next year, so everything Gas Powered releases before then is yours to keep. If you like the game a lot, that will probably be worth the deal.
One note of warning: Gas Powered also says that buying the Season Pass won't keep you from rebuying content accidentally, so don't forget and buy more stuff when your Christmas cards come in. But hopefully if you spend $100 on a free-to-play game, you won't really be tempted to spend any more than that, right?