I don't know about anyone else, but I for one am a metro UI purist. I love me some of that metro UI design, like the Zune PC software, or some amazingly well done apps on Windows Phone like zbox or readit or the apps Rudy Huyn has made. The UI of those compilations of code hit the hammer to the nail of what the metro UI is all about fundamentally: Typography. It's not about live tiles, it's not about crazy colors, it's not about full screen apps. It's about typography and interacting with the typography. It's about the digital motion of the UI. It's about not using skeuomorphic iconography, nor glassy window borders that detract from the contents within that window.
Windows 10 is showing further expansion of the modern UI design (I've noticed when it was officially called "modern" UI, the subtle richness of the metro UI went away) but is drifting away from the roots of the design philosophy. There's no focus on typography, at all. Even Windows Phone 8.1 took some of that away. On Windows Phone 8 with Xbox Music, you were able to wake your phone, tap the current playing song from the volume control, tap on the artist name header line on the Now Playing screen and it would take you to the album collection you have by that artist and from there play a different song or album. Simple and easy. It's doesn't do that anymore in 8.1, well, kind of but you end up with the album of which the song is from and can't jump around to a different album. There is no digital motion at all whereas on 8 it was just so simple and so beautiful when you interacted with the UI from the Photos hub or showing the Start Screen. That is what the visual eye candy is with the metro UI.
It's about being wowed by everything within the window altogether. I always recommend trying out the Zune PC software version 4.8 to truly understand this. At a glance, it seems bare and minimal, but when you use it and interact with it, you end up appreciating the gracefully well designed UI it has that is also quite practical.
But this doesn't go to say Windows 10 doesn't have some of these principles, the fact that the window bordering is pencil thin is essentially the meaning of content first with the window control buttons being more like simple markings than icons keep content in focus.
There is so much potential for the UI to improve. I'd like to see more design going forward that keeps in line with the principles of the design language Microsoft created that is now basically becoming rather common with software and web design. A little bit more of digital motion is needed. Better use of typography and focusing on typography is desperately needed, as it chucks out more skeuomorphic bits like the switches.
A modern operating system needs a modernly designed user interface.