At the moment, quite disappointed to be honest.
Lost an hour and a half of my working day when pressed the upgrade button - this on an i7 with 8 logical processors and a SSD - so obviously a big upgrade.
However; thus far the only change I have noticed is where I used to click Start and type one or two characters, to get my application shown on the short list to run; I now only see Microsoft applications, until I get to 5 or 6 characters, at which point I get to see the application I actually want to run.
Sorry Microsoft, but as an Engineer, 90% of the application you supply Windows 10 with are of little or no use to me, I need to use third part applications to do my job. That is now that little bit less efficient with 1909.