The most significant change Microsoft made to Windows 95 was replacing Program Manager with a more Macintosh-like UI, but notably featuring a menu button with the word "Start" on it.
This is why the Windows logo menu button is still called the Start Button today.
Microsoft marketed the heck out of it in a TV ad campaign 25 years ago today: https://www.youtube.com/watch?v=CVd_NyQ7-Aw
Anyway, happy silver anniversary, Microsoft Windows 95!
One last thing on this thread: The Computer Chronicles episode about Windows 95 after boxes were available: https://www.youtube.com/watch?v=ZBbvmORcgSo