Valve have released a video demo of their Steam Controller in use. The video showcases a small variety of games to give you a feel of what it’s going to be like. Personally I don’t think it will replace my keyboard and mouse but I do look forwards to crushing joypad users on any FPS games.
As far as a controller goes, I like the look of it and I’m going to be open minded to at least try it, probably more so with single player and local multi-player for myself. Enjoy the video and make up your own mind.