Much like their new desktop update, iOS 9's focus is largely on the fit and finish and some much needed improvements to their core apps. One of the big features is "Intelligence" which makes iOS smarter with upgrades to Siri and will even do things like recommend a recipe if you search type in Chocolate Cake in the search bar.
Apple is also making some big updates to their apps and introduces a new one. You'll see enhancements to Notes with drawing features, an all new Passbook which is now called Wallet, new and improved Maps with transit integration, and a brand new App called News that adds a Flipboard-fighting article reading experience to the iPhone and iPad.
You'll also improve graphics performance, improved battery life, and you will see some big upgrades to the iPad side with features like new multitasking features, Split View, and even a Picture in Picture feature that lets you watch video while inside another app. iOS 9 will be available for public beta next month and the official release will hit this fall.
More at apple.com