After almost a day with iOS 9 on my iPhone 5s, I must say I'm a bit disappointed performance-wise. Animations are dropping frames where they didn't before - examples: Control Center (worst offender for me, feels like a 4s running iOS 8, and even my iPad 4 on iOS 9.1 beta is smoother), Cellular section in Settings (terrible scrolling performance, feels like Music.app on iOS 8.4.x or the early days of iOS 7), Spotlight "pull down" gesture (janky, janky, janky - was so smooth on iOS 8.x; turning off Siri Suggestions doesn't help) and keyboard "slide in" animation (dropped frames while writing this very post!). Safari scrolling inertia is also screwed, feels terrible to scroll through long pages.
What I do love about the update: content blockers (oh yes!), "back to" shortcut, proactivity regarding audio connections - such as headphones or Bluetooth speakers (genius!) - and all the app enhancements (small touches in Music and Mail, great new capabilities in Notes, News app - even if I feel it's quite slow).
What I do love about the update: content blockers (oh yes!), "back to" shortcut, proactivity regarding audio connections - such as headphones or Bluetooth speakers (genius!) - and all the app enhancements (small touches in Music and Mail, great new capabilities in Notes, News app - even if I feel it's quite slow).