Not once have I had an issue on my desktop. Its stable, plays all my games, old and new.
Now that my graphics card is no longer receiving driver updates, I have had to stop windows prompting me to upgrade to the latest package, but that's just a sign I need a new GPU soon *cough*polaris*cough*.
I also bought a surface pro 4 in march this year, the second-bottom model with i5 and 4gb ram.
I've had some issues, widely reported. Sleep of death, touchscreen and camera failures. I think these are more Surface issues than Win 10, however.
Overall, a great upgrade. I just hope they continue to improve things!