We bought a new laptop last Christmas which came with W10, so we had an opportunity to see what it was like.
I then upgraded my PC to W10 about 3 months ago (I had downloaded the free version it but not installed it - but it then gave me a date (about 4 weeks notice) when it was going to install it automatically, like it or not - so I just went for it). It all went seamlessly, (took about 30-45 minutes from memory) and all my files and desktop shortcuts were transferred across without a problem.
I don't actually use the PC for a lot - Word and Excel (it kept the original 2010 versions), internet access and games like Solitaire, FreeCell. I use Chrome for browsing and AVG for protection. I've had one or two issues with AVG subsequently but I'm not sure whether that was some conflict with W10 or just a problem with AVG.
I have not run into any major problems with it since upgrading, just a few niggles. The first noticeable thing was that the PC boots up much more rapidly.
It's set to do Windows automatic updates, but these seem less frequent than on W7 and take longer when they occur.
My gripes would be that the thing revolves around "apps" so it's much more modern than I'm used to! To get the games package (which is excellent, contains Suduko and Mahjong), you have to go to the Windows Store and download the "app" which is free - but, you do get regular adverts when you play them, and these can only be removed by Upgrading, which costs (something like £8 a year). I was playing as a "Guest" but it hectored me to sign up for "XBoxLive" which means you have a gamer tag and your games are saved in the Cloud, but an unexpected side-effect from this was that it then implemented user password protection on booting up the PC (not a problem, actually more security in a way, but I hadn't asked it to do that!)
It also keeps nagging me to "sign in" to my Windows 10 Account (i.e. the Store account), but I cheerfully ignore that and it goes away.
There have been criticisms in the press that it's sort of Microsoft controlling you via W10 rather than you controlling your PC via W10 .... I can see where this criticism is coming from, and I do find that its messaging can be intrusive.
I didn't like it at first compared with W7, but having got used to it, I can live with it - it's fine for what I use it for.
Just my 2c worth .....