This update contains improvements and bug fixes, including:
CarPlay
iOS experience designed for the car
Simply connect your iPhone to a CarPlay enabled vehicle
Supports Phone, Music, Maps, Messages, and 3rd-party audio apps
Control with Siri and the car's touchscreen, knobs, and buttons
Siri
Manually control when Siri listens by holding down the home button while you speak and releasing it when you're done as an alternative to letting Siri automatically notice when you stop talking
New, more natural sounding male and female voices for Mandarin Chinese, UK English, Australian English, and Japanese
iTunes Radio
Search field above Featured Stations to easily create stations based on your favorite artist or song
Buy albums with the tap of a button from Now Playing
Subscribe to iTunes Match on your iPhone, iPad, or iPod touch to enjoy iTunes Radio ad-free
Calendar
Option to display events in month view
Country specific holidays automatically added for many countries
Accessibility
Bold font option now includes the keyboard, calculator, and many icon glyphs
Reduce Motion option now includes Weather, Messages, and multitasking UI animations
New options to display button shapes, darken app colors, and reduce white point
New Camera setting to automatically enable HDR for iPhone 5s
iCloud Keychain support in additional countries
FaceTime call notifications are automatically cleared when you answer a call on another device
Fixes a bug that could occasionally cause a home screen crash
Improves Touch ID fingerprint recognition
Improved performance for iPhone 4
Fixes display of Mail unread badge for numbers greater than 10,000
Continued user interface refinements