The main reason I decided to buy a Steam controller was because, after playing a lot of Rocket League, my fingers started to hurt. As a controller for that, it's not particularly good because clicking in either touchpad, the bumpers or the control stick require a considerable amount of effort. As a controller it feels a little tacky for that reason, the fact that you can feel the ridge around the side with your hand and that the plastic doesn't feel too good.
That aside, the rebinding capability is absolutely immense. I did some calculations a month or two ago and I think you can fit up to something like 80 bindings on it, if a lot of them aren't frequently used. If there isn't a community binding you can modify to fit what you want you can always start from scratch, and do wild shit like turning haptic feedback on or off, adjusting deadzones (including removing deadzones the game already has), changing trigger start ranges, adjusting feedback curves and now you can even do macros. The amount of sub menus there are in the "configure controller" screen will keep you entertained for days if you're into that stuff. They're constantly updating the software from user feedback as well, such as adding in support for the gyro and clearing up the UI to make it easier to work with. Oh yeah, you can also add games to your steam library and use controller bindings there, but you have to launch it from Big Picture.
There's a few other things that bug me about it though. If you start any game with the controller plugged in/on, it launches the steam overlay in big picture mode, which is an absolute arse to navigate with a keyboard and mouse. Furthermore, if you have that overlay, whenever you open a text box in game it'll bring up the controller text menu, which covers the whole screen. If you want to quickly type a message to someone via keyboard but keep an eye on the game, that's impossible. However, if you then choose to launch without the controller plugged in, then plug the controller in, you can't edit the bindings at all. Anyway, these might get fixed in time.
Anyway, there's a wall of text

By my standards, £40 (or your regional equivalent) + shipping is a bit steep for how long I've used it for, but hey, I can always sell it on. If it sounds better than an xbox controller, don't let me stop you buying one, but I haven't really had any experience with other controllers such as to give a decent comparison
