I've been testing Windows 10 since October 2014. I've been in the fast ring since March, 2015. My initial experience was that it worked better and was more stable than when Windows 8.1 was on this machine. I have seen some minor bugs, but nothing that would stop me from switching right now. I do, however have my reservations about Spartan. There are some key features missing that I use often, like a home page button, and I have also had issues with the settings actually working. For instance, it seems to go to any of the options sequentially when it starts. One time it will start at the page I closed it on when last in use and another time it will go to my selected home page and yet the next time it will open with Bing as the home page. I have it set in the settings to open my desired home page, Google. This to me is a minor flaw in an otherwise wonderful operating system since I use other browsers as my main browser. With Windows 8.1, I had many problems with trying to use 2 DVD/BluRay optical drives in my machine. With Windows 10, those troubles are gone, completely. The only other issue, and this was fixed easily and works much better than any other system I had it on, is my company supplied VPN connection. My company wouldn't support it, of course, but I searched the Internet and found the fix quite easily.
It takes a while to load or update, but your patience is rewarded with a solid operating system. I am running it on an AMD quad core with 8GB of ram and 2, 1 TB internal hard drives with a third used as a backup and hooked up externally by USB. I have 2 optical drives, 1 BluRay R/RW manufactured by Pioneer and the other a DVD R/RW by Samsung. I log in using my old Microsoft fingerprint reader and a modified driver I found on the internet. I do not have a touch screen monitor. I use a Insignia 32" 1080P TV and an HDMI connection. I am currently on build 10130. I guess you could say that my system is your basic home PC.
I suggest that if you want to install and use Windows 10 preview, you should make sure you have a link in your Internet browser of choice to the Microsoft Windows 10 forum. I have found a lot of useful information there and fixed several of the minor irritations I have encountered. Oh, and yeah, the settings app needs some getting used to. Fortunately, control panel is still around at this point to help the adjustment.