I thought I'd copy my impressions from the other thread:
I just received mine today. I play almost exclusively with mouse and keyboard, and with the exception of specialized input devices such as HOTAS, it's easily the best solution for almost every problem. My reason for this purchase was in part due to curiosity and certain cases where a controller may be of use.
I spent several hours across various titles and use cases. I tried some that had official support, and others that did not. First of all, I will say that this isn't a replacement for your mouse and keyboard. I didn't have any illusions of it being otherwise, but I thought I'd make that clear. That said, after my hours of play, I find that it's better than a traditional controller in almost every way. The level of precision and speed is unlike anything you can accomplish on analog sticks. Even with the right pad alone, it's already an incredible leap forward, but further adjustments with the gyros or dampening features, allow you to move even beyond that. Even the ones without official support, after making a configuration, I was able to achieve great results. The community bindings aren't a bad place to start either. I don't know how anyone could sustain an argument where this isn't significantly better in anything related to camera movement, aiming, or cursor control, at the very least. The one possible exception in favor of traditional controllers is games where you extensively use the D-pad for movement, but I haven't played enough of these on the Steam controller to say for sure.
The ergonomics and button placement, while different, appears intentional in that it's designed to avoid having to move your thumb away from movement and camera controls entirely. The presence of the two back buttons reinforces this. The thumb isn't meant to rest flat on the pad, but used with its tip, hence the concave design.
Additionally, the fact that this controller is even viable for games that could never be played on traditional controllers is incredible. Of course, even many genres that were once considered not to be viable with traditional controllers have become so, but at the greatest expense, negatively affecting game design. If the Steam controller's pads were to be adopted by the console manufacturers, this could solve a lot of problems. Of course, that's a big if.