The app icons are mostly terrible, and the control center/quick settings menu feels like they never quite got around to polishing it up. It is overall a massive improvement visually though. Some of the transition animations could do with being about 30-50% faster. They look nice, but they add a slightly frustrating delay when you're hopping back and forth between various apps and screens quickly.
My iPhone isn't a daily driver though, just a hand-me down I mostly just use in my music dock.