The rounding is not bad. There are excellent examples in the form of Material Design or macOS.
But it annoys me that, according to the good old Microsoft tradition, the implementation will extend over the next 2 years and will appear in the Windows elements in a very selective way, and a bolt will be put on the part.
Here we have Fluent Design, class. Yes, it's nice, but how many different contextual menu options have already been accumulated? Win32 with blue highlighting, in Start with white highlighting and white highlighting, in Explorer with white highlighting, but without effects, in Settings with gray highlighting, shading and dark highlighting … And I haven't even finished listing.
How many have waited to blur the taskbar background? And when did transparent transition accent lists appear?
And how will they turn the windows? I'm not sure that the cropping will be performed as on macOS. How they broke the boundaries of Explorer, so the second version is not repaired, where it is the rounding.
… so the idea is not bad, but it should be multiplied by the Microsoft implementation. And in my opinion, it would be better not to know.