To each their own but I found their new redesign to be excellent and as someone who uses a fair number of their products, I've never had any issues differentiating one from another based on their icons.

For starters, each product has a distinct icon color, which in and of itself makes a huge difference in usability and the ability to quickly determine which icon to click. This is something the Google redesign fails completely on.

Secondly, every element behind the single-letter in each MS icon has distinctive elements that are related to the product. Excel actually has grid-cells to mimic worksheets in a minimalist fashion. Powerpoint has the pie-chart. One-Note has the fantastic minimalist binder with tabs in the background.

Between the unique color and graphical elements associated with each product, there is plenty that helps a user easily distinguish one from the other while they all still have a cohesive aesthetic.

I find it to be an outstanding redesign. In comparison, the Google redesign basically has almost none of the benefits above and makes it a lot harder to distinguish icons at a glance.