Metal has a lot of features that make it a good choice to use in your 3D graphics app or game. Here you can find a list of features of Metal:
It provides extremely low-level access to A7 and A8 GPU to enable high performance to your graphics rendering.
It eliminates a lot of performance bottlenecks, such as state validation, that is found in most common graphics APIs.
It is designed to be efficient with Apple hardware to ensure the highest speed with low overhead.
It provides up to 10x number of draw calls in your app compared to OpenGL ES.
A big enhancement in game is load time performance, thanks to the support of precompiled shaders. They're an incredibly important part of rendering a realistic gaming experience. Precompiling enables them to load faster.
It is designed to move all expensive operations and creation of objects to be outside the runtime of the game loop.