InstallationAfter downloading, it gives you 10 seconds to choose if you want to install now or later. If you don't choose, it installs now. It takes about 30 minutes to install and restart.
Updating resets your usage counters!
NotificationsYou can now dismiss banners by swiping upwards! Previously, you had to wait for them to disappear before you could tap on things at the top, e.g. Safari address bar.
Notification Center is now divided into "Today", "All" and "Missed". I think these headings could be better named.
Today shows your schedule. In Settings, you can customize Today View to show a summary, your calendar, reminders, stocks, etc. and confusingly, "Tomorrow Summary".
All is notifications from apps, etc. - what Notification Center was previously. Counter-intuitively, All is not all. It doesn't seem to show your schedule!
Under Messages, there's an option "Show Alerts from Everyone" or "Show Alerts from My Contacts" - what exactly is considered an alert? Play a sound? Vibrate? Notification? Does this mean if I set it to only my contacts, it'll only play sounds and vibrate for messages from my contacts? That might be just what I need. UPDATE: If you set it to from my contacts, it still plays a sound when you receive an SMS from someone else. Not sure what this does.
Use Mobile Data For:Found in Settings - Mobile. You can set whether individual apps can use mobile data, and see how much data each app uses. I love this feature! You can save data and battery, and even block ads. You can block specific apps while leaving the rest.
It no longer shows you mobile data sent and received separately, now it's just Mobile Data Usage. But now it also shows you data used while roaming.
Background App RefreshThis is a bit confusing - there are now several lists of apps in Settings. Mobile data, above, background refresh, space used, privacy, and more. This controls what apps can do when running in the background. Nice, but not as useful as the mobile data one.
Block ListIt now has a block list that you won't receive calls, messages or FaceTime from. Like a permanent DND. However, I don't think I'll use this as I still want to receive ads from some companies, or what if someone on your block list changes their number, and someone important now uses the blocked number? I'll stick to my silent ringtone instead.
RemindersYou can now show completed reminders. I couldn't find this before. This is useful if you have a checklist you want to reuse, e.g. to fly a plane, turn on engine, release brakes, trim something.
Color-code lists (but you only have 7 colors to choose from).
CalendarI miss the old calendar, which would display a list of events for a day. This calendar can only display a timetable, making you scroll through empty times. It's easy to miss early or late events. UPDATE: If you go to month view, it'll show a dot under days with events, like the old Calendar.
Camera/PhotosCamera now has burst shooting, at unknown FPS. This means you can no longer take a photo when you release the on-screen shutter button, making it slightly harder to compose/steady the camera.
Photos are now divided into Year - Collection - Moment. These photos appear to be taken from your Photo Stream. I still need my Camera Roll to see which photos I haven't transferred yet.
Yes, videos you take are still found in the Photos app.
App StoreApp Store now shows the apps you last updated, which is nice. App Store doesn't support system's Text Size setting. Come on, Apple!
MiscellaneousThey said no more skeuomorphisms, but I distinctly see Notes still has a paper texture. And I miss the lines on the paper.
The unlock sound has disappeared, and the lock sound seems to have gained an echo.
The top bar doesn't say "LTE" anymore, it just says "4G". I guess WiMAX is out? I wonder if it still says "E" and "O", and what they mean.
It now says my (third-party) cable may not work with my phone (but it still works). Online, some people say their cables have stopped working totally.