I spent 4 hours yesterday eagerly updating my iPhone 7, iPad Air 2 and Apple Watch 2 to the new iOS 11. That was 1.5Gb for the phone and tab and 600Mb for the watch. Here are some of my thoughts -
the new keyboard for the iPAD is a huge improvement. Apple's keyboards are some of my major frustrations after moving from Android. You always need to switch to get numbers and special characters which makes choosing secure passwords a pain.
Unfortunately the iPhone keyboard was not improved and you still need to switch to get numbers and special characters and punctuations.
I quite liked the screen recording feature (hidden in the Control Centre settings), but I am not sure how much this will actually be used.
They finally added Mobile Network to the Control Centre. This will save me days of my life as I switch between Wi-Fi and Mobile Data.
The new Watch Activity App has really been improved. I like that I can now switch types of workout midway through my session, because I usually do cycling and running in the same workout (Discovery Active Reward junky)
I like the extra Heart Rate stats from teh watch.
I still cannot initiate a WhatsApp message from the Watch (only reply on an incoming notification).
Nice to make Gifs from your Live Photos (although I hate it when people speak in Gifferish)
I use Siri quite a bit, but have not tested enough yet to comment. I really hope that you can get contextual commands instead of keep having to say 'Hey Siri' to give the next command.