I did an upgrade from 8.1 on HP laptop. Probably should have gone with fresh install but I had a lot to lose if I had chosen that route.
First, I believe MS has rolled a lot of fixes since the release. I will list the issues I have with Win 10 so far:
a) I, like everyone else, always close the lid to put my laptop to sleep. 7 out of 10 times, if I open the lid to wake the machine up, it crashes/restarts. I've noticed that that happens if there is a connected device (like a phone via USB or TV via HDMI cable).
This is my worst annoyance/bug so far.
Impact: Highest/Major
b) Battery life in laptops: Win 10 consumes too much power.
MS and Intel were to release a fix. Not sure how far that has gone. Or if it's my battery that has issues. I can almost swear I used to get an extra hr with Win 8.
Impact: Major
c) Calc: When I press Win Key+run then type "calc", the calc app does not show the first time. I have to execute the sequence again for the app to be actually opened. Really pisses me off.
Impact: minor to major depending on my mood
d) The fingerprint reader sometimes just fails for no reason. It blinks, I swipe the finger, thinks for a few seconds, then continues blinking. No error, nothing. Secondly the thing is always blinking. On win 8, the reader would only blink when it detects a password field.
This may be a vendor issue, not necessarily MS. Still, considering it was working well in Win 8 I would say that something broke with the upgrade. I'll keep watching out for an update from either MS or HP. Not very optimistic about HP, though.
Impact: minor to very minor
e) VLC and change of screen outputs: This may not affect office users. I noticed that when playing a video file with VLC on a second screen using the extend screen option, if I change the project option (to PC only, Second Screen only, etc) VLC video feed freezes. Audio still comes out though. The only way to get out of it is to restart the VLC. Again, not necessarily a win 10 issue.
Impact: None on weekdays, Very high on weekends
It now takes over 15 minutes after restarting the machine for it to be completely useful. This could be related to disk performance (it's always at 100% until after the said 15 mins), applications, background services, OS optimisation or any combination of factors. I cannot pin this on Win 10. Just wish I had done a clean install to know for sure if it's a Win 10 issue.