Almost everything. The colours, the flatness, the overreliance on animation to reveal cues that have been hidden by removing too many of the useful aspects of colours and depth.

Material design is a company led attempt to create a fad a la Metro. They'll keep trying for about 18 months before they create a new one where it's back to bevels again. Just don't expect any of the non-Google apps to follow it, in the same way that all previous efforts went wrong.

Incidentally the number of U-turns by Google on this stuff is incredible. We were previously told explicitly not to attempt doing physical analogues of motion etc. as those didn't map to the app navigation model . . . but now that's exactly what they want.

What really grates though is just how the developer experience for all this stuff seems to be going backwards.