It does actually mention this, about halfway down:

One of the major points of criticism is that overusing Claymorphism and going overboard with colors and typography can give off a somewhat childish feel to the UI. Michał Malewicz acknowledged this drawback and gives a few suggestions on how to avoid that.

    “The friendliness of those shapes, along with the 3d imagery creates a slightly child-like interface. To counter it, it’s good to use minimal typography, strong accent colors good contrast.”

    — Michał Malewicz

There is still room for criticism though since this style of interface is not "somewhat" childish. It is the design language of Fisher-Prize, of large colourful plastic toys for toddlers.

If foresee a trend in classical Russian literature inspired user interfaces as a reaction. The Dostoyevsky style, dark and deep.