Happy with mine, minimal lag, only thing I'm noticing is a lag on unlock screen, I'm normally quick to press that first digit but on iOS 9 it's not registering that first press so I have to delay for a few seconds to press. No big show stopper though.
I skip IOS 8 on my Old reliable Ipad 2 (because of some bad review) so I decided to stick to IOS 7. But yesterday I took the plunged and tried IOS 9 with clean install. And, all I could say is, my Ipad 2 was born again. It feels like brand new again and it is more responsive than the aging IOS 7, and best of all, now I can use Apple music on my ipad.
Battery on my iPhone 6 is much better than before. At a certain point in the day my battery would be at around 50-60%. These last two days, I'm finding myself between 70-80%. Might be coincidence, but I think not. If anything would have thought I'm using my phone more which would yield a lower battery life.
Battery seems to be behaving better on my iPad too.
Very happy with iOS 9!