Here is a decent review of watchOS 10:
https://www.macstories.net/stories/watchos-10-the-macstories-review/
The main 'innovation' is the smart stack of widgets that you now get by swiping up (or scrolling up via the Digital Crown). By default it is populated by automatically selected items but you can pin as many of the 'widgets' to the top as you want to get your own chosen list of widgets.
Widgets are summarised versions of apps (ie, they show a portion of what the actual app would show) as well as means to launch the actual apps. You can also have a widget that shows three complications.
In a sense, where previously you could swipe left and right to get to different watch faces that, via complications, showed content from different apps and thus also served as a way to launch apps via this, now you you swipe up to see a set of sort of larger 'complications'.
Why they had to remove the left-right swipe method to add the up-swipe method, however, is a mystery (well, some say that too many people accidentally swiped left or right and unintentionally changed their watch face and that is the reason why they removed this functionality).