Well, for one the Control Center taking up the entire screen in landscape mode is just ridiculous. As a frequent gamer, it's annoying to have to swipe down (and sometimes accidentally swiping to the Music controls) instead of simply tapping out.
The second page media controls is really getting on my nerves too. I started using my device at iOS 10, and I've also seen the iOS 9 CC, and to be honest, the iOS 9 CC really looks a lot better in terms of ease of use and arrangement.
Just my thoughts on the CC now. Really, it's not unusable or anything, it's just a little annoying sometimes.