For my money, this is (so far) the best quick-highlights view of iOS5:
Many of the new features in iOS 5 are things we've been sitting, waiting, and wishing for since the iPhone first launched. Complete with a more robust notification scheme and a brand new messaging protocol, Apple has filled in many of the gaps that have left it behind other OSs like Android and webOS.
In particular, I think the notifications changes are interesting.? The first take on notifications was visually nice but just didn't scale - as though designed for people who would get the occasional push notification or SMS text.? But the reality is that some people get too many push notifications to count in a day.? A new approach was needed for a world where all the apps leverage the notification system as well.
With messaging - and Apple made note of this during the keynote - there was an oddity in that iPads and iPod Touches were left out of the messaging game.? And it probably rankled that BlackBerry had their own messenger product that would soon also work on iPhones, and would also bypass the SMS toll booth.
Business Insider has a good series of screenshots of the new features, but without much commentary or analysis to go with it.