First of all, the Steam Controller is not a replacement for your mouse and keyboard or your Xbox/Playstation controller, it instead a compliment to your "arsenal" when it comes to control schemes and setups. Instead of thinking of this as a replacement, think of it as a middleground between precision and comfort. It doesn't beat out a keyboard and mouse when it comes to precision and it doesn't beat a controller for some games, at least initially. With the unlimited configurations that can be set up, the limit is not the controller, but simply how hard you are willing to get the perfect setup for you .

Please note, that this controller is not for everyone. The controller has unparalleled customization which is a blessing for me, but for others, it could be a curse. While you can get presets from the community, this is only the tip of the iceberg. This controller is mainly for tinkerers, who love trying to get that optimal setup and constantly testing and customizing their setup, improving their experience as they go.

In addition to this, you do need to get acclimated to the controller, which may keep some people from using it, but once you get used to the controler, it gives way to a wholly unique control scheme that is well worth getting used to.

The Steam Controller does have many strengths, though. The paddles for a start, open up a lot of options for new setups and control schemes. You can bind relatively hard to reach buttons to the paddles which really drives home the idea of comfort. In addition to the paddles, the controller has gyro controls (like the WiiU gamepad) this has many uses including fine tuning for aiming in FPS and steering in racing games.

I have found that the Steam Controller works very well for certain genres of games and decently for others with little to no setup time. With these games, the Steam Controller is easily better than controller or keyboard+mouse. These games are the following:

Third Person Action Games:
-The Witcher 2 + 3
-Metal Gear Solid V The Phantom Pain
-DMC Devil May Cry
-Metal Gear Rising: Revengeance
-Bayonetta
-For Honor
-Assassin's Creed
-NieR: Automata
-Middle Earth: Shadow of Mordor

With these games, you can do everything that a controller does, but have more mouse-like movement for your camera, without sacraficing any comfort, which makes everything much easier and pleasant to play.

2D Platformers:
-FEZ
-Nidhogg
-Rayman Origins
-Strider
-Inside
-Shovel Knight
-Ori and the Blind Forest
-Speedrunners

All of these work very well because of the D-Pad/Trackpad on the left side of the controller. With this, you can simply slide your finger across the trackpad to move, instead of the typical joystick controls on most controllers. It gives some unparalleled comfort once you get used to it initially.

Everything Else:
-Borderlands 2
The built in aim assist for BL2 can really help you get accustomed to FPS on the Steam Controller.

-Project Cars
With the gyro steer, you can sort of get the feeling of a steering wheel on a budget. The haptics in the controller create a switch-like HD rumble in the controller, so you feel every bump in the road, and every pebble. Gear shifting with the paddles is also amazing.

-Super Mario Galaxy
If you can get your hands on an entirely legal copy of Super Mario Galaxy, I would wholeheartedly reccomend this on the Steam Controller. You can use the gyro controls built into the controller to move around the cursor, as well as the standard controller feel for a Nintendo game.

In conclusion, the Steam Controller is an impressive piece of hardware that has near unlimited versatility that is only limited by how far you are willing to go. You can play just about anything on this thing, but you will have to put in the work for some stuff to get a great experience.