OK, here are my experience about Win10 sofar (about 1 day).
The upgrade (not clean installation, simply over my Win7) and activation went well without issues. No driver's problem or whatsoever. Win10 runs stable.
The activation has some issues yesterday evening, perhaps because Microsoft server was overloaded. The activation went in a jiffy this morning without any problems. No new keys or whatsoever was required.
I had Win8 and 8.1 but rolled back to Win7 due to massive GUI issues, I hate it totally.
Win10 solved quite many but not all, some settings jump between normal Windows settings (control panel) and Win 8/8.1 Metro UI settings without you even really notice it. If you accidentally landed on Metro UI settings you can not go back to normal control panel that easily but you must click control panel again all over again from start.
The active apps on Metro UI and normal Windows applications are still separated just like on Win8 /8.1.
The issues, which I hate on Win8/8.1, are still there.
The Metro UI not as dedicated screen but only part of start menu, well, I kinda like this. The normal Windows apps are also there, good job here.
The stupid gesture e.g. moving mouse cursor to certain edges and pull down, etc. are gone on my PC settings, I like this.
Turning off/on your PC is a bad implementation on Win8/8.1 but the one in Win10 is back ok.
The Win10 GUI stuffs give me a bit of a mixed feeling, it is better than Win8/8.1 but not still as good as Win7.
I agree with those who said that Win10 is actually only Win8.2. Win10 still sucks in GUI point of view, just like Win8/8.1, although the GUI on Win10 is still better than Win8/8.1.
I hope Microsoft will still patch things to fix those I hate. It does not have to be like Win7, something new is ok but just not like the current Win10.
At the moment, the killer implementation on Win10 for me, which I really hate on Win10 is the update service is that you can not control the updates like on Win7. I guess the update will be set always to automatic (at least I have not found a way to change the settings). I wanna have it to inform me and let me choose which updates to install.
Now to the question, if I want to keep Win10. Well, I dunno yet, I wanna let Win10 active for a couple of months first than decide.