The biggest user end inprovement in Win10, compared to Win8(.1), is the unified user experience. Out with the schizophrenic tablet-desktop-whereamI-whoamI-whatamIdoing experience. There is not tablet UI separate from the desktop UI, at least not when running windows on a regular laptop PC. I won't say anything about Windows tables since I do not use them. The start menu is an actual menu again, a combination of menu and start screen. I really like it!
Notice the Power and Settings at the bottom of the Start menu? Another yey for those instead of that annoying right hand side hover manouver of Win8.
Search has been separated from Start to its own "menu", opened with the magnifying galss in the task bar, next to the Start icon. Windows + S shortcut key also still works.
Really, those are the biggest changes in the UI, for the common user. The only thing that truly annoys me in Win10 is its tendency to do random restarts while being in sleep mode.