So, if the idea behind icons is to quickly locate the tools you need, even if you are not super-familiar with the tools, I think the previous icons served that purpose much better.
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.
Even if I had memorized what every icon means, I can't tell them apart without looking closely because most have the same shape and similar colors. "Everything looks the same" is not good design.
If that is not clear, here is an example of Microsoft Office's excellent execution: https://medium.com/microsoft-design/redesigning-the-office-a...