I received a new Windows 8.1 OS last year, which had the built-in opportunity to update to Windows 10 at any time for free. I didn't want to make this decision though, because 8.1 was doing fine and I heard rumors that it takes a while for the system to adapt. Now however, the free offer will end at July 27, so if I want to upgrade to 10 efficiently, I only have this month to do so.
Personally, I really like 8.1, so I'm mostly interested about the drawbacks of not upgrading, but all personal experiences with Windows 10 are welcome.