It's a relatively minor update, a list of the main changes can be found at the Windows Blog. Among other things, there's new Edge stuff like an integration of web tabs in Alt + Tab. The Start Menu and the Taskbar have also been refreshed with a more streamlined, less colorful design.
A refreshing Start. The Start menu has a more streamlined design. A uniform, partially transparent background to the tiles creates a beautiful stage for the redesigned app icons like Calculator, Mail and Calendar. This refined Start design looks great in both dark and light themes, but if you’re looking for a splash of color, first make sure to turn on Windows dark theme and then toggle “Show accent color on the following surfaces” for “Start, taskbar, and action center” under Settings > Personalization > Color to elegantly apply your accent color to the Start frame and tiles.