Metal. If the name sounds hardcore, it's because it's a hardcore improvement to the way games perform on iOS 8. Metal represents a much more no-nonsense approach to getting the most out of the Apple A7's gaming performance, assuring users of the iPhone 5S, iPad Air and iPad mini with Retina display that their devices will continue to be top-notch game systems, along with the iPhone 6 and iPhone 6 Plus, and everything to follow.
In iOS 7 software called OpenGL ES sat in between the game and the core hardware that ran it, translating function calls into graphics commands that are sent to the hardware. It's a lot of overhead. And iOS 8 provides a much more efficient way to do it.
Draw calls, used to render all the objects in a scene in a 3D game, are up to ten times faster on the same hardware when using Metal. That means much faster, more responsive games with incredibly detailed environments.
iOS 8 gets a bump in game load time performance thanks to support for precompiled shaders. Shaders affect how an environment is lit and colored; they're an incredibly important part of rendering a realistic and immersive gaming experience. Precompiling them enables them to load faster.
With game developers always pushing the complexity envelope, this helps improve the user experience; after all, you don't want to sit around waiting for the game to load on your device.
Another benefit of Metal is to provide developer access to the compute power of of the graphics processing unit (GPU) embedded in the A7 and A8 processors. In the right hands, this could be one of the most important aspects of Metal.
Enabling such access to the GPU means applications can be more thoroughly optimized for parallel processing.