I think one thing conspicuously lacking here (besides rounded borders and gradiented buttons, both of which aren't part of Metro style) is icons. Nowadays most sites use icons to add visual interest to plain text. Microsoft's old designs didn't, and I think they suffered for the lack of them. The new design is refreshing and clean but would still benefit from having some similarly clean and functional graphical elements, i.e. icons.

(Crossposting to their feedback.)