For example 'visual clues' in the Classic Windows have minimize and maximize buttons and the "X" button means close. These Modern GUI Windows, where are the 'visual clues'? It breaks the way Windows is supposed to work.
You have to drag the mouse to the bottom or top right side of the screen to access the 'Charms Bar' to do stuff in it, and Windows-C as a shortcut. I tried the touchscreen and it is a nightmare trying to make the correct type of swipe. Sometimes it does things you don't want it to do.
Plus a lot of desktop apps cannot be converted to Modern GUI mode because it lacks the gadgets the desktop has to make things easier to use. The Visual Studio IDE for example has so many tool icons and toolbars that not all of it will fit in a Modern GUI screen. It would need a major rewrite of the GUI, and force all developers to relearn all of their Visual Studio skills.
Remember when Office 2007 made that Ribbon bar? It was worse than Clippy the Office Assistant type of annoying.
Many compared Modern GUI to New Coke, the Classic Version was always better. If not for Desktop mode I could not use my Windows 8.1 Pro device.