Jim Hamm installed OS X 10.11 -- El Capitan -- on his MacBook Air on September 30, when it was released. It took about 30 minutes to download the 6 GB program, and another 40 minutes to complete the install. All went well as far as he could tell at the time. His MacBook Air has an SSD, and it must have been working hard as the cooling fans were blowing hard to cool the Mac down during the install. Normally he does not hear the fans. According to Gizmodo (here) there are 11 things that can now be done that could not be done with Yosemite. Another recap of the new features of El Capitan is given here from MacRumors.
One new feature is the ability to find the cursor by just shaking the Mouse. It is sometimes difficult to see where the cursor is located.
Microsoft has said there will be no more major updates to Windows 10 -- just continuous improvements. Will Apple follow their lead?