Wet with anticipation for Valve's Steam Machine? While you're wishing for Santa Gabe to gift you the machine of the future you can witness YouTube user Trial By Game demonstrate a bunch of games played with the Steam Machine's controller.
There's a bunch of games that have been demonstrated with the controller, from those that would work perfectly to those not so much. Above is Rogue Legacy, and below you can watch Typing of the Dead, DOTA 2, and Super Meat Boy, with plenty more over on the YouTube channel.
All in all the controller doesn't look that bad!