I didn't notice anything drastically improved. The cut/copy/paste/delete icons in the context menu threw me off for a bit. Kept choosing more options, before I realized they were along the top. It took me awhile to realize I had to right click on the menu button instead of anywhere on the taskbar to get a menu where I could bring up the task manager and other stuff. I gave up on the Windows 10 menu so I couldn't care less about the changes there, though it looks different for sure. The absence of the power mode slider (for my laptop) from the battery icon in the notificationr is the most annoying thing I've encountered. It's now buried in the system settings. I leave it in performance mode and let the fans go wild unless I'm on a conference call or watching a movie. Switching is now more tedious. So, overall nothing drastically ruined either.
I didn't have to reinstall any apps or drivers. I just used the upgrade assistant to kick off the upgrade and it basically ran until it was done. Afterwards, I did some incidental cleanup of install files, checked over that things were still working, and that was about it. Nothing was broken for me so it was quick. Obviously, if you're going to do a clean install it's going to take a lot more work.