Update: it doesn't exist anymore.
The Steam Controller is officially abandoned by Valve. I will still leave my opinion about it here, because reasons.
So you dislike the Steam Controller...
The Steam Controller is out (for those of you living under a rock: Valve, creator of Half-Life and Steam, created a game controller that is meant to change gaming forever). And it is mostly awesome.
In reviews all over the internet, I often read things like "the pads need to go away", "who needs a gyro", "the Xbox360 controller is better", "nobody will ever use this" and so on. Written by people who spent like an hour or two with the device.
What those people don't get is: this is not just "yet another controller" but rather an entirely new kind of device. At least parts of it. And this of course means you have to re-learn it from the ground up. How long did it take for you to type with 10 fingers? You get my point.
Why is mouse & keyboard bad?
Mouse and keyboard aren't bad at all. If you are sitting at a desk, that is. But once you move to the living-room, things get bad. Either you sit at this low table near the couch with your back bent like a monkey or you try and balance the keyboard on yourself while mousing on the side of your leg, or maybe spread mouse and keyboards to the sides on the couch, occupying the place of like 5 people.
Why are standard controllers bad?
Standard controllers are pretty good for some games and pretty bad for others. For example first-person shooters. With the mouse, you can turn precisely within a fraction of a second and aim perfectly at the guy creeping behind you. For the controller, this means pulling the analog stick to the side and waiting for your character to turn. Probably dying in the process. Or try (yeah, you really should!) playing some real-time strategy with a controller.
Why is the Steam Controller better?
Simply because it combines the accuracy and versatility of a mouse with the ease of use of a standard game controller - and throws in some nice extras.
Dual trackpads with haptic feedback
The most obvious feature are the dual trackpads. No, they are not like your flimsy laptop's trackpads. Fingers slide easier on them because of the rough surface and they emulate a lot of different input devices, giving haptic feedback while they do.
Trackpad emulation
The most obvious one: they work like traditional trackpads. Nothing special here.
Trackball emulation
A heavy arcade-style trackball is emulated. Fling it and it spins, put the finger on it and it stops again. And you can feel the rolling motion by a faster "ticking" the faster it spins.
Analog stick emulation
Does what it says. Move your finger on the pad and the emulated stick moves. Haptic feedback is available here, too. Clicks on several angles of the virtual stick. The fun begins when you add an extra function to the "outer ring". If you move your finger all the way to the border, a modifier key can be automatically pressed. Like sprinting.
D-Pad emulation
The name gives it away: areas on the pad are defined as the four buttons of a D-Pad. And opposed to what nay-sayers keep shouting: you can customize it to work flawlessly. And be fast like with a classic D-Pad.
Touch menus
You can configure a trackpad to act as a menu. So when your finger touches the pad, an on-screen menu with up to 16 items in a grid appears and the absolute position of your finger on the pad is mapped on the menu. Yes, this means you can use these menus without even looking. Of course you can use modifiers, so the pad normally is for moving (for example) but while the modifier key is held, you get a menu instead.
Activators
With activators, you can add even more functions to a single input. Sounds crazy? It is, but in a useful way! Imagine a space sim, for example. On a "normal" controller, you would maybe use the right shoulder button for "increase thrust" and the left one for "decrease thrust". With activators, you can define a "long click" that goes to 100% thrust for the right one and 0% thrust for the left one, for example. Double click and a few others are also available.
Action sets
Playing a game where different actions would require different configurations? Like the menu, walking around and driving a car in GTA? You can define action sets, which basically are completely separate controller configurations for one game, and define a key to cycle through them or automatically change it based on the mouse pointer being visible.
There is more
I'm just writing about the options I actually tried. And by "try" I mean using it for an extended period of time, getting used to it and taking a good amount of time to configure.
Alternate mode
Each pad can have two control schemes. A modifier key (you can freely choose which one it is) switches to the alternate configuration. Like precision aiming while zoom button is held.
Dual stage triggers with mechanic end switch
The triggers have a short throw (which you do get used to, stop nagging!) and a wealth of configuration options. A few real-world examples.
Racing games
When using one of the analog triggers for acceleration, the tactile end switch can be used for nitro. Pull the trigger all the way back and you have a "kickdown".
For braking, the tactile button can be the handbrake.
First person shooters
You often have one button for zooming / looking through the scope and another one for shooting. Put both on one analog trigger and choose the right "hip fire" reaction profile to suit your needs. So if you pull the trigger fast to the clicky button, you shoot from the hip and if you pull it slowly, you zoom in. Leaves the other trigger free for grenades or other hotkeys you may need at hand.
Grip buttons on the bottom side
Two additional buttons for those things you need the most without loosing aim in a hectic situation. Like jumping or reloading. Your fingers stay on the pads for movement and aiming.
Gyro
The critics say it's stupid, like a Wii controller thrown in and that you can't use it for anything. Well think again. What works awesomely well (although it sounds strange, I know) is using the gyro for precision aiming in first person shooters.
Look at anyone playing a game with a standard controller. You will notice everyone moves the controler around in tight situations although it doesn't make any sense. With the steam controller, it does. Because you can use this natural movement, this "go a little more to the left now" irrational movement of the controller and use it for actually moving the character. So you likely are already doing it, and now it starts making sense. Finally.
For first person shooters, I have the right trackpad set to trackball (because you can very quickly turn for a controllable angle which you can't do with an analog stick) and the gyro to go the last inch with much lower sensitivity. After a few hours you get used to it and start thinking "how could I ever use that shabby old standard controller for such a game?"
Games I tried with the Steam Controller
Planetary Annihilation: Titans
Planetary Annihilation: Titans
I tried "Planetary Annihilation: Titans" with the steam controller. I have to admit I am not too good at strategy but I do know how to use a mouse and keyboard. And with the Steam Controller, it took only a few hours to get the same speed like with mouse and keyboard. What I liked was moving on the planet. I used the left pad with two modes: one moves left/right/up/down and the other uses it as a wheel, turning the view. The right pad was a standard trackball.
Serious Sam 3
For this game, I set up the left pad as analog stick with "sprint" on the outer ring, the right as trackball and the gyro as mouse, active only if the finger is on the right pad. Left grip for jump, right grip for reload. Took a while to get used to it, but it is definitely possible to rush through hordes of enemies and actually hitting them. The occasional long-range shots are easy. Before the steam controller, I tried it with a standard controller and ended up stuck in a level with lots of enemies in confined space. I just died all the time because I could not turn fast enough and still be able to aim.
GTA 5
It was a pain in the ass to install and doesn't play well with Steam, changed controller configs need a restart of the game, but that's not a problem of the Steam Controller but rather a problem of Rockstar Games. Left pad: analog movement with sprint on the outer ring, right pad: trackball, gyro: mouse. Right grip: special ability (the bullet time modes). I had to fiddle with the anti deadzone setting for the left pad to make steering at high speeds possible and smooth. Tried a modifier key for the gyro to act as left analog stick for very precise steering which works great, but the left pad doesn't react anymore afterwards. Definitely a bug.
Grid 2
For this racing game, I made two action sets. The first action set is a default game controller with both pads being the sticks and the analog stick of the steam controller being a copy of the left pad to suit both playing styles. I mapped the left analog trigger's end switch to "handbrake", but the rest remained default.
The second action set is a copy of the first one, but with permanently-active gyro. The gyro only affects the left stick's horizontal axis, so it only steers and does not scroll through vertical menus. I haven't beein using trackpad or stick for steering since I added this gyro action set.
Gemcraft - Chasing Shadows
For this game, you need a lot ofdrag'n'drop and hitting the same on-screen buttons all the time. I used the right pad for trackball, the triggers for the mouse buttons, the select button cycles the game speed and the alternate function for the right pad, using the left grip button, is confined mouse movement. The right pad is limited to the gem creation area, the left pad triggers the spells.
Elite Dangerous
This game is hard to get right because they screwed up the menus, IMHO. For flying, I used the gyro for mouse steering only while the right grip button is pressed, doing a "center mouse" when the button is released, and the left pad for the remaining axis. The shoulder buttons increase and decrease thrust by 25%, a long click of the "decrease" button zeroes thrust. The "B" button triggers the boost, a long click triggers SuperCruise. Y toggles through the surrounding ships, the analog stick is for power distribution and all the functions that you only need occasionally like landing gear, headlights, frame shift drive and so on, are placed on touch menus of both pads.
The ship's menus are triggered with X+Analog Stick and there it gets tricky. The analog stick (configured to the cursor block on the keyboard) cannot be used to navigate the menus just like that because they screwed up. So I put a second touch menu on the right pad with a modifier key that gives me all directions, the page left/right buttons, OK and Cancel. It is a bit of a workaround but it works pretty well.
For a game that uses most keys of a standard keyboard AND the mouse, I'm still surprised how well it works with the Steam Controller.
X Rebirth
For X Rebirth, I used a similar setup to Elite Dangerous, but the mouse aiming was a little tricky because you have to keep the mouse button pressed for it to work. The mouse button is also used for clicking ships and stations and landing pads in space, necessary for example for docking. So I used a button to toggle the mouse button for easy flying and another button to do normal clicking, allowing it to override the toggle. It is not 100% intuitive but it works very well after an hour or so.
Wrap-Up
If you actually want to know how this controller compares to others, then use it exclusively for at least 20 hours, take at least half an hour to get the configuration right, take your time for the pad rotation, reaction curves and deadzones and forget everything you know about controllers. You will be rewarded with something that actually brings gaming to the couch. No, you will not win tournaments against keyboard-and-mouse gamers. But you will begin actually enjoying gaming on the big TV screen.