I just picked up a steam controller during the summer sale and I absolutely love it. Honestly my biggest gripe with it has been the analog stick it has, which should have been either an 8 input dpad or more buttons.
I've noticed the biggest critics of the steam controller have been those plugging it in and expecting to play right off the bat. Once you actually learn how to use it you realize, much like how analog sticks were initially a "gimmick" until they became an industry standard, so to will the trackpads. They are capable of emulating so many inputs, sometimes better than those actual inputs(IE the analog sticks), and paired with the gyro motion controls and haptic feedback...you realize the negativity levied against this controller is from those who just need a standard configuration and a game to learn how to use it.
If you go back to when both single and dual analog hit the market, people had the same complaints about how awkward they were to use.