It's pretty good on my 6+.
I am with the 10.1 beta, and the battery life is great. I intentionally test the battery life by charging it to 100% and then use it for +24 hours. Normal use, auto brightness, with all LTE, Wi-Fi, BT (Apple watch paired)...on, and let it goes into low power mode when the 20% low battery notification appear. Sure it's enough for my one day use.
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I upgrade to iOS 10 mainly because I want to use home kit, and WatchOS 3. And end up it's a good decision. The OS is smooth (not as good as my wife's 6s+, but sure no unacceptable lag / shuttering).
And I love them open the API for 3rd party apps to identify the rubbish phone call.
I personally prefer the iOS 9 notification centre, but not a big deal for me. Also, I am OK re-learn few new iOS 10 stuff. However, I am sure this is very personal. Someone may feel the iOS 10 looks really ugly.