I haven't dug into everything yet, but overall I'm positive on it. I love how much snappier everything feels (I'm on 6S Plus). I'm enjoying the new look of the notifications and am even cool with the widgets page being off to the side because instead of having to pull down and then pick left or right, you can either pull down for notifications or swipe for widgets. Pretty smart.
The whole removal of swipe-to-open is going to take getting used to. I've had moments where I was annoyed by having to basically double-click but other times it seems to work well. Jury's out on that. I do like raise-to-wake to avoid the phone just blowing me onto the home page when I'm trying to just look at my lock screen (first world problem of a blindingly fast TouchID)
I do miss the pull-down reply to incoming-text banners that seems to have given way to a sort of halfway opening of the Messages app. Not sure if I'm describing it right, but it used to be when a text notification dropped down while the phone is unlocked, you could pull it down just a smidge further and get a little blank cursor to type a quick response. Now pulling down on it opens a fullscreen card with a full view of Messages. Just feels slower.
I'm also shaky on the Music app, which looks a lot blander and less exciting/colorful than before, but whatever, as long as the music plays.
I'm generally happy with Messages, though I doubt I'll get a ton of use from all the new apps and stuff for it. I'll send an emoji once in a while, but I don't see myself sending cartoons and scribbles and things very often, but I'm sure a lot of the kids love it.
I love that I was surprised last night with a message from Maps telling me where my parked car was and letting me know it had dropped a pin there. Interestingly it didn't do that when I went to work or went home.. only did it when I stopped somewhere unusual. ***** brilliant, honestly.
I still have a lot more to dig into and check out, but overall everything feels a little faster and I do love that folders and everything are animated much faster than before.