This is exactly backwards - all of the iOS 7 complaints I've heard so far have been about the UI polish and not the underlying functionality. Polishing a turd would be a beautiful UI in front of a buggy, slow system. Apple didn't ship a polished turd, they shipped a rough, unhewn diamond.
But each major iOS version is slower than the one before, it's just that we got used to it (and loud people on the internet always use recent devices anyway). I think this blog post is a good example of something that is definitely a polished turd. A clean, beautiful UI for a resource hog:
And something else that we have accepted is that Apple's services are what they are. For example, iOS 7 has polished the Photos and Camera apps. But in the big picture, Apple's ecosystem for photos is still a complete mess. There is Photos.app with its own Camera Roll, iPhoto for iOS, Photostreams, Journals, Moments, iPhoto '09 with its own Events, and no sane way to keep everything in sync.
