Some issues I have with W10:
1. Upgrading from Win8.1 my new account no longer had admin rights. I looked on the internet and found out you have to log in as a local user, which automatically gives you admin rights, then log back into your MS account and that carries your admin rights with you. Took a lot of time to figure that out.
2. You cannot move your OneDrive files to your SD card. You could in Win8.1. After upgrading, I only had about 11GB left on a 64GB drive on my tablet. But with my OneDrive files synced offline, I only have 3GB. Again I looked online, but the only tip I found was that in order to change file location, you have to unlink and relink OneDrive so that you go through the OneDrive setup screens again...but still, cannot use SD Card as a OneDrive location...even with admin rights.
3. You have to have admin rights to use the disk cleaner, if you want to delete your windows.old folder (my solution to getting more HD space. And yes, I made an image of my Win8.1 setup before I upgraded, just in case). So again, I had to take a bunch of time to figure out how to resolve my #1 problem.
4. There is an option in the Settings-System-Storage menu to download apps to another drive other than c: ...but it's greyed out. uhm...why? Also, when there are other options to save new stuff like docs, pictures, music, and videos to the SD card...that works fine...except it seems to default back to c: by itself for some reason.
5. Mail app doesn't seem to be working for any of my accounts. No email is downloading, even though I'm signed into my accounts. I still have to look on the internet to see if I can figure out why...but there is only so much time I have to devote to this in the last 3 days I've had Win10 installed.
6. So many buttons!! For a tablet?! The main concept for using a tablet was to swipe this, swipe that, with minimal amount of buttons. I just looked at my friends Ipad (because something was wrong with it and they needed my help), and it looked simplistic by nature. I'm sorry but simple always wins out with the masses. for example Look at common appliances in your house. Take a washer and dryer...most have simple buttons and dials. Sure there are people who know how to take it apart and figure out how to fix it and how each component works, but not the masses. Simple buttons and dials wins out, and they will come and buy it. Win8.1 was rather simple looking compared to Win10. Sure IPad is even more simple looking, but my wife (who is no computer expert) was able to learn Win8.1 after some simple tutelage for me, and configuring her 8.1 tablet to work better for her (Move her OneDrive folder to the SD card, as an example). I'm looking at Win10 and thinking to myself "How am I going to teach her this?" Fortunately, MS has a year to clean it up before I may upgrade her tablet with the free upgrade. But if MS doesn't clean it up better, maybe I prefer leaving her at win8.1. Remember folks, your tablet will probably be replaced before Win8.1 support is dropped.
In conclusion, I think Win10 looks promising. The above items could be fixed, conceivably, within the free year upgrade. But, typical of all Windows releases, not quite ready for primetime, but good enough if you are computer savy and can spare the hardware to install this on and play with a not-quite-there-yet OS.