I was a bit worried after reading some of the reports, but this release seems fine so far to me. Performance-wise it doesn't seem worse than iOS 8.4.1 and it may even be a bit faster.
The battery life isn't great, but it never was particularly and the phone seems quite cool most of the time, the exception being when hammering wifi. But note: I do have some bits disabled (e.g. background app refresh). I can well imagine that with different bits enabled, running different apps etc., that your experience might also be different to mine. I do not wish to generalise.
Battery stats:
5 hrs 7 mins usage
5 hrs 56 mins standby
battery 44%
Most used app iTunesU (44%, mainly watching video lectures).
I was hesitating to install this because iOS 7 -> 8 wasn't a great experience for me, but then after watching this video I was encouraged somewhat:
So, thus far a moderately positive update for me and, if iOS 9.1 can improve on this, then I think I will be content. That is, assuming nothing nasty materializes.
So, if you're undecided, I'd say give this a try and see how it works out for you.
Good luck!