It's comes with the console, all the necessary cables, such as mini-usb to plug it into your PC etc, and 2 controllers (batteries included).
The games are free-to-play, so after you buy the console that's all you have to pay for. Games such as Minecraft, Temple Run, Angry Birds and you can even watch Twitch TV live streams with an app. Various apps are also available.
Think it will be worth buying, even if it's just for the novelty. Can hardly go wrong with the price, and there seems to be many decent games available. You can also customise the console freely, so if you know how to add more RAM, new processor, graphics card etc then you're free to do so. If you're some mad hacker, they have no problem with you fiddling with your own console.
http://www.ouya.tv/
Few videos:
Specs
1GB RAM
8GB Flash Storage
Bluetooth 4.0
1080p HD output
USB 2.0
HDMI
Tegra 3 Processor