Honestly the only real change is the command center, which is basically all the same stuff in a new layout. There are some new animations and larger font in your email. The only real change is all the emoticon and gif and sticker changes. A new app store as well, just really boring.
So I am starting to think what @jmanz said about the battery life is true. I use to charge over night go all day and still have 75% left. Yesterday when I got home I had 4%. Today is slightly better but still going down faster tha iOS 10.
After installation yesterday things seemed faster (6 plus) and battery seemed better or same. Today some things seem like already slowing down and battery is at 62% but that's normal for a 30 month old phone and the use of it.
Testing some more right now and truthfully, things seem snappier all around for the apps I use. Myfitnesspal, to log calories since a fatty, used to be terrible but now it's so much better. Same for others.
I also like some of the additions to the OS. Biggest thing is when I go to storage it lets me bring up a list of what items are taking up what and where they are. Take videos and pictures in messages. I try my best to clean them up myself but keep so many and would be a pain to go through old message threads to find what and where they were. Now it does that for me and tells me. So nice. Also the offload unused apps may be nice to use for removing the app but keeping the data. Before it was all or nothing.
Ya I need to just go through my settings. I know there is a portion that shows what is using the most battery. I like some of the darker fonts like on the dial screen. There is one big change that I have noticed. That is the clarity of my calls. I first noticed this yesterday when I made a call to a dealer, I thought man they sound crisp. Then I talked to my wife today and there was a big change, normally I can't even understand her, but today she was clean a crisp. I wonder if there was a change?
So far the battery life has been I would say just slightly worse. About a percent or two difference (worse) after the update as of about 12:30. I tried to keep the usage about the same to get an accurate test. Not as bad as I was expecting so far.