Overall it has been fine, however there are many nuance issues to be dealt with. For example:
1. Screen Sharing has changed, a where I use to initiate the connections, and can do so if I am sharing my screen but I need to have the other user initiate for them to share their screen. Have not determined if this is a "security" feature or a settings issue.
2. Desktop clutter is an issue that causes screen lagging. Once I cleaned up my desktop it is not an issue, but under the previous OS it was not an issue.
3. The redesign of the launchpad, and inability to customize app location on screens takes getting use to (but IMHO -sucks)
4. Customizing the toolbar in Apple Mail is not working properly. Still trying to determine if this is a setting issue, or a design flaw from Apple.
The ability to customize is at best less intuitive, at worse not available. That said I have not seen a significant flaw or issue to impede upgrading with one caveat. If the user is of advanced age, or needs routines the changes in the OS and ability (lack of) to tweak could be an issue.