It is rock solid. I really enjoy it so far, however I am going to advise everyone to NOT upgrade at this point.
There are a ton of built in trackers that can all be turned off, I don't really have a problem with this. Win10 appears to be streamlined to work on laptops, tablets, phones, and desktops without any real changes needed. Which is good in my opinion.
The problem I have currently, is even if you turn off/ block every tracker and aid out there, Win10 will still send in to MS everything you type into the Start menu, as well as any installed Bing searches. (I don't honestly care about Bing searches, every search engine compiles what you search for, this is nothing new, and will continue as long as we have search engines)
Here is the kicker, within the USA, this is in direct violation of several credit card protection laws, as well as HIPAA.
Here is an image of what is sent: http://imgur.com/dB0sruf