AirPlay; much better multi-display support; tags in Finder; Spotlight enhancements. More than anything, the iCloud/iOS continuity features were also big if you had an iPhone or iPad, everything is just much easier to keep in sync.
I'm a Safari user (better battery usage for the # of tabs I have open) and it too has improved with El Capitan though that's irrelevant for Chrome/FF users.
I'm a Safari user (better battery usage for the # of tabs I have open) and it too has improved with El Capitan though that's irrelevant for Chrome/FF users.