I also bought a steam controller too and i stopped using it because the mouse joystick is pretty bad for fps games (IMO).

The mouse joystick is not very sensitive to slight movements of my thumbs. Thus, its basically impossible for sniping. It is possible to configure the joystick like a normal gamepad joystick but then I require really low sensitivity to aim well.

I figure it would work better on other kinds of games. Probably my favorite feature of the controller is that u can make the controller aim the camera with movement. Thus moving the controller up moves the camera up :D.