Introduction - Material Design - Google design guidelines
http://www.google.com/design/spec/material-design/introduction.html
Google states two goals at the outset of their ‘Material Design’ spec.
1. Create a visual language that synthesizes classic principles of good design with the innovation and possibility of technology and science.
2. Develop a single underlying system that allows for a unified experience across platforms and device sizes.
After reading the whole doc, I would say this: Sure, it’s a visual language. It is far, far more prescriptive than Apples HIG. And the synthesising and science and metaphors are a little ridiculous. It’s simple, thoughtful and user-focused. A step in the right direction, absolutely, but it’s no design revolution by any stretch (not that there has been one since iOS 1).
What it does do, and does really well is hit that second goal. It’s very clear that every decision here is made with multiple screens and devices in mind. And for that, it is kind of revolutionary.