Of course I've seen valve's original video, I am quite a fanboy of the steam controller so far

I am into the steam controller not for playing on a big TV (i don't have one and don't plan to buy it yet), but playing on PC in 1...2 meters away from the screen. Currently I play using x360 controller on my PC, which is very comfortable and immerse for me for games that have good support for it (i.e. GTA IV, Skyrim, Assassins Creed, ...). But Steam controller is aiming to support any game. The biggest advantage of a handheld controller is that my hands don't have a fixed position - I can move them around and sit in any pose I like, while having your hands on the table attached to the keyboard and mouse makes my hands and my back tired after a couple of hours.