FIFA 12, Battlefield 3, Star Wars The Old Republic, Kingdoms of Amalur: Reckoning... all of them require Origin to be played. Origin is more than a simple way to play online games, it also offers an online shop to buy downloadable games for a reasonable price.
One of the main advantages of Origin is the possibility to get all your games backed up onto the cloud. So, in the event you have to format your computer or you buy a new one all you have to do is hit download to get all your games back.
In addition, the platform comes with some free games in it which are honestly pretty good: Battlefield Heroes, Need for Speed World and Battleforge are just a few of the titles you'll play for FREE.
Origin still isn't a major site like Steam, but if EA keeps launching exclusive games on Origin, it'll grow day by day.