The design gives no indication of what's clickable. Reminds me of those Flash games where you frantically click on things trying to find out what does something. Except now, everything is a flat-shaded rectangle.
The input side seems confused. In their guidelines, they talk about buttons having a drop shadow, and less shadow when depressed.[1] Fine. But not all buttons have a shadow, and not all objects with a shadow are clickable. On interaction, they write "What will happen if I touch this screen? And then this icon?"[2] That's a game-like interface. It might be tolerable if there was an standard, easy way to undo whatever you just did. There's no sign of that in the guidelines.
There are 84 standard input icons.[3] But no icon dictionary. Help text is so last-cen. You're supposed to know.
When they finally get to "Buttons"[4], they have a reasonable set of controls. However, one of them is plain text, with no indication that it is clickable. That contradicts their principles of material design. If they're going to have all this pseudo-3D, it ought to be used for all things which behave differently from their surroundings. But no. Google does suggest the use of a distinctive floating action button for "promoted actions" (i.e. "Buy").
The output effects are pretty, but that's all this is. Pretty. It's all output-side. There's no innovation on the input side. It's what you get when you put graphic designers in charge of a user interface.
[1] https://www.google.com/design/spec/what-is-material/elevatio...
[2] https://www.google.com/design/spec/animation/responsive-inte...
[3] https://www.google.com/design/spec/animation/icons.html#
[4] https://www.google.com/design/spec/components/buttons.html