The unboxing: The controller felt light out of the box. The controller takes two AA batteries. One battery goes into the left handle, the other into the right. This adds a little bit of balanced weight to the controller. The A/B/X/Y buttons feel really small (think mini m&ms).
The setup: This went easy. I plugged the wireless dongle into a free USB slot and I was ready to go. But wait, how do I navigate big picture? There was no indications on how I navigate big picture, so it was a little bit of trial and error. My first thought would be that you navigate with one of the touch pads, nope. It turns out you use the thumb stick to navigate with. I would have thought it would be the touch pad (isn't this one of its selling points?).
The controller: I like it. It feels comfortable to me. I really like the grip buttons. The small A/B/X/Y buttons don't bother me. The touch pads are just like a trackpad on my computer. Haptic feedback seems like a gimmick to me. I don't feel like it adds anything.
The games: I tried three games out. Portal 2, Starship Rubicon & Borderlands 2. Most of my time was spent with Borderlands 2.
Portal 2: I picked this game due to it having native steam controller support. The first mode I tried was gyroscope for mouse look. I knew this would be gimmicky, but I wanted to see if my gyroscope worked. Yup, it worked and I quickly turned off this mode. :) I then switched to right touch pad as mouse look and thumb stick as movement. The mouse look drove me nuts, as it was always fighting me and wanting to go to the upper-right. Later on I revisited the game, and it worked fine, so something must have not been set up right. My second visit to the game worked out ok. Again, it feels like I have a trackpad under my right thumb.
Starship Rubicon: I picked this game because of Cheerful Ghost. First up, Starship Rubicon does not recognize the steam controller as a game controller, so I could not use Starship Rubicon's native game controller support. I ended up using the keyboard and mouse setup for the steam controller. It took me a while to figure out how to bring up the on screen keyboard to enter my pilot's name. Once I did, it was a very interesting experience. Left touch pad is your left hand and right touch pad is your right hand. You pick the letter you want and then push the corresponding trigger button to enter the letter. Game control is on par with a trackpad and controller. I find that since I don't know all the keys this game needs that I need to remap the controller as I go. Example: I needed to map the left-shift button. Overall it is better than playing on my macbook air with its trackpad and keyboard (which did not go so well :) ).
Borderlands 2: I used the game controller with mouse setup, which is what steam recommended. This works out fairly well. I find that I am not used to the touch pad sensitivity out of the gate, but I am getting better at it. The right touch pad is your mouse look, while thumb stick controls your movement. The right touch pad is set to trackball mode. I find myself running out of touch pad on occasion as I hit the edge with my thumb. I think I will get better with it over time, as I am already seeing some improvement after a couple hours of use.
Overall I like the controller. I really like the grip triggers. It is a keeper for me.