How has matchmaking crapped the bed this badly in S4?

Like it was great pretty much from the mid-point of Season 3 until Season 4 launched when it's taken an absolute nosedive. It went from fairly balanced and fun matches frequently to like 6-8 games of absolute curbstomps followed by 1/2 good games then back to crap again.
It's actually kind of maddening. Because neither stomping nor getting stomped is fun, especially not this often.