Now that iOS 8 is in the hands of developers, we'll likely be getting a lot more detail. Apple was able to give only a very cursory overview during the keynote. Macworld has posted an article on 20 features that Apple didn't talk about during the keynote. Some of these are pretty cool, such as time-lapse mode for the camera, private browsing tabs in Safari, battery usage by app, and more. The article covers detail related to features of Camera, iBooks, Siri, Safari, Settings, and Calling.
In addition, AppleInsider has posted a first-look demo video of the new Health app in iOS 8. Apple's introduction of the HealthKit platform and the Health app was very brief, and the AppleInsider post and video give helpful detail regarding what the app does. Basically, it's a repository for all of your health data. According to the post, Health has four sections: Dashboard, which gives overall metrics using a card-based presentation, MyHealth, into which you can enter your personal data, Medical ID, which will hold information that would be needed in an emergency, and Sources, which is the aspect of the app that collects data from external devices. Companies such as FitBit are partnering with Apple to offer compatible devices.