Sluggish UI, broken sleep, telemetry, advertisements in the start menu and lock screen, forced reboots and general "computer doesn't obey you" design philosophy.
Also just lack of attention to detail. e.g. if you start to search in the start menu and then delete what you typed, you don't get the base menu back; you get "suggestions". So e.g. if you search for "power" or "shutdown" to power off, don't see it as a result, and delete your search, the power button won't be there anymore. You have to close the start menu and open it again to find it. Completely ridiculous design (KDE by contrast has the button and finds the action as a search result with both of those search terms).
Also just lack of attention to detail. e.g. if you start to search in the start menu and then delete what you typed, you don't get the base menu back; you get "suggestions". So e.g. if you search for "power" or "shutdown" to power off, don't see it as a result, and delete your search, the power button won't be there anymore. You have to close the start menu and open it again to find it. Completely ridiculous design (KDE by contrast has the button and finds the action as a search result with both of those search terms).