'Material Design' primarily diverges from Metro around the use of drop shadows, gradients and lighting effects. Where Metro avoids these 'fake' effects as part of it's authentically digital mantra, Material design is embracing them as natural cues that we're pre-programmed to recognize.

I won't disagree with the Metro influence but I think this separation in design philosophy is incredibly important.

The Material approach has sometimes been called 'almost flat' design, and I think it really embraces the criticisms raised in articles such as: http://www.matthewmooredesign.com/almost-flat-design/ http://gizmodo.com/designers-shadows-are-totally-fine-in-a-f...