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Email improvements include better photo and video attachment support, funky new pull to refresh animation, and the ability to assign VIPs to your email. VIPs are synced via iCloud too so they will appear on your iPad and iPhone as well.
Shared photo streams: I never found much use for photo streams, but now with the ability to share custom streams to family and friends it makes sharing photos much better.
Guided access: This new accessibility enhancement helps people with disabilities, such as autism, remain focused on content. It can also be used by parents to limit an iOS device to one app and restrict touch input to certain areas of the display. There are other features in Guided Access to help blind and low vision users too.