I've been on windows 10 since the early releases. It is quite stable now however there is a annoying bug with supercruise when using AMD graphics. It is a driver issue that AMD looks to be addressing. The is the only issue I have seen that has caused me any real grief.
So wait to upgrade if you don't want to take the plunge yet....but remember the free upgrade ends 1 year after release so upgrade before July 2016(July 29th was the release date)
I am just a "basic" win user (i mean, i do not know anything about the system, i just turn it on/off and play games

) and i upgraded to win 10 from win 7 months ago (i do not remeber when).
I did not find any problem, issue or whatever. Everything runs smoothly, fast loading, no crashes.
I can imagine they gave the update for free for some reason, mainly getting our informations, but i really do not know how to stop that so i gave up and accepted the unavoidable: Microsoft is stealing my data.
That said, IMHO, from a basic user point of view, Win10 works perfectly.