Well, the free upgrade period from Win7 and Win8 is only supposed to be for 12 months, right?
Disadvantages are mainly in the form of privacy. By default, Win10 wants to know
everything about you and
even includes a fucking keylogger. Blah.
There are guides to fixing some of those issues but even after taking all those steps it still frequently phones home...
something. No one's sure what.
From a gaming perspective, expect better performance since Windows 10 is even more lightweight than Win8 (which was more lightweight than Win7).
I personally made the upgrade to Win10 but disabled all monitoring and invasive settings. Make sure if you create your account to not use a microsoft/live account as that enables some extra snooping that can't be disabled in the settings.