This.
It's all in the detail, and the details in iOS7 are all wrong IMO.
Minimalism on the one hand; that crazy 3D picker control and parallax effects on the other. Fonts which are either too fine or too thick.
Someone mentioned the clock, saying "oh, it's not hard to understand". No, it isn't hard, but it isn't as obvious as it was. Again, it's details; subtlety. Windows wasn't particularly difficult to use, but it did sometimes become a bit awkward and non-obvious.
Everyone who I've spoken to about the update (like, 10 people today) has mentioned the fonts and the calendar app. No good words about either.
iOS7 feels like a Microsoft product. There, I said it. It's not that the overall design is intrinsically bad, but it's missing that Apple X-factor.