Good list of details and photo gallery from CNet on the major goodies in iOS 8.
iOS 8 by itself simplifies and enhances features you already had in iOS 7 and adds more conveniences to the apps you already know. It’s not a drastic change like the redesign in the previous version, and it’s not even as big an overhaul as iOS 6. But it is definitely something you’ll want to download for the improvements it adds across the board. Just keep in mind that its most promising features may still be in development.
What isn’t mentioned is how much of an upgrade iOS 8 is for app developers. Within the next six months iPhone users will have thousands of extensions and widgets available.