Steam Controller Review
It's a very good controller. The structure is rigid and feels reliable. Pieces fit well together and nothing feels sloppy. Structurally it avoids any details that aren't utilitary.
Structure
The most noticeable feature in the steam controller is the backplate that fuses with the grip buttons. It forms the button caps and covers the battery compartment while hiding and protecting the product detail inscription under the plate. It's actually clever. The backplate got a small spring plate under which will push the cover from the place when you pull a small switch aside it. The hook locking that piece under seems to be reinforced in two directions, so it needs to be heavily mistreated before it breaks.
It's shaped from the bottom just like an ordinary controller, but on the frontside the handles raise to sink into your palm and support your thumbs. It is very comfortable. I wonder how Sony managed to go through many designs for their playstation controller yet failed to figure this one out. In the bottom the controller got four holes with hexagonal screws in them. I suppose you can open the whole thing and put it back together with no problems.
Part of the frontside has different finish, I'm not entirely sure why. It clips and doesn't continue to the backside. Maybe the idea is to let fingers slide or rest on that part of the surface?
Controls
The second most noticeable detail in the controller are the two circular touchpads that are concave a little bit, such that they sunk about 1mm on their centers. The left-hand pad has a rounded cross engraved onto it. These are the neatest thing in this controller once you get to configuring. They shake to give you a tactile illusion about whatever they represent at any time. It's not anything like moving a trackball, but I like it more than a trackball. It also feels very much more precise than a trackball.
Pressing the joystick, trackpads, shoulder bumpers, dual stage triggers and grips give out a loud baby food jar lid sound. You can almost use it to clicker train your dog, though it's not louder or more annoying sound than mechanical keyboard keys. On the frontside there's a four-button-squad, two arrowed mode-buttons and one double-size central-button that lits up and resembles Iron mans reactor. Those ones are quiet, comfortable to press and do not deviate from their locations on other gamepads for no good reason.
The analog joystick with it's rubbery head isn't interesting. The rubber gives a nice grip, but the joystick itself is just an ordinary analog joystick.
Gameplay
You can find extreme cases where the steam controller will fall flat. Just pick a game that uses every key on the keyboard or try use it to draw with gimp. So far I've successfully played counter strike, portal 2, dosbox and old emulator games with this controller.
The old descent was a disappointment because the thing didn't recognize the steam gamepad as a joystick. Otherwise it might have been pretty cool game to play. I also tried dota 2, and it seems to be playable with this controller, but as a game it doesn't seem like anything you could just fire up and play.
In terms of how good it is at simulating mouse control, I think mouse can be more precise but I prefer steam controller over a mouse for other reasons. A laptop and a steam controller could be a nice combo because laptop keyboards and touchpads consistently suck. Though even in front of a full desktop with office chair the steam controller allows very ergonomic posture.
Most games require some configuration, but I've found it quite natural to do all the configuration when the game requires to do the given action for the first time.
Control virtualization
I feel this controller sets up a new genre of gaming controllers. It's the first one that can reconfigure itself while you're playing, giving more dynamic gameplay with more intuitive controls than what was previously possible.
The idea seems to be that despite what the game developer does, the end-user says the last word about how the gaming controller behaves. You are supposed to be able to adjust how the controller behaves while you're playing a game.
It's also the first one that I've seen which lets you decide how it presents itself to the games. It will become your mouse or keyboard if the game doesn't have joystick support.
Biggest flaw
I've had some early-adopter issues with non-steam games. If the game jumps from smaller screen into a big screen, it loses the config before you get to play. For that reason sometimes you need to set a desktop config manually when you want to play a game with weird behavior.
The biggest flaw in this controller is that there's no apparent way to program a completely custom behavior for the controller as an user. For example, you can put the analog stick to pulse-width modulate with arrow keys, pretending that you have analog input even if it's just repeatedly pressing buttons for you. It's neat but it doesn't seem to take into the account that the joystick head is limited in a motion to a circle. Therefore with current analog emulation you can't do full diagonals. And you can't fix that yourself. You got to wait for Valve to act.