The steam controller is thicker than the xbox 360 controller. This controller has track pads instead of the analog stick with the buttons in the middle. The Buttons, a,b,x, and y are in the middle of the controller where the ps3 has their start button.
This controller is the same weight as the xbox controller. In the middle of it is a high resolution touch screen. You are able to save games and do more with this touch pad.
They have the kit for this controller. Valve did not test it out yet on normal games such as call of duty, killzone, and more. They did not release a price for this controller.