The introduction of iOS 6 about UI changes and some new APIs.
With the screen shots, you can understand what's the difference between the iOS 5 and iOS6 at one glance.
What’s the difference in iOS 6 Redesigned with a more friendly UI Other apps can access and share lists Forget Google map, it’s iOS map now Create audio for interactive web app New feature about reminder and no disturb Focus, exposure and region, also face detection API
iOS 6 for Developers Facebook integration A) deep integration with Facebook B) more way to connect and share by adding Facebook C) using SLRequset to access user’s account
iOS 6 for Developers Reminders “Your app can now access and share to-do lists in the Reminders app. With the Event Kit framework, your app can create and modify reminders, assign properties like due dates and priorities, and even set location and time-based alarms.”