Now I am sure there have been countless reviews of this since the technical preview has been out for like a year.
However here is my take as someone who never used the technical previews.
I upgraded one computer from Windows 7 and the other from Windows 8.1
1. The upgrade was a breeze. It downloaded through windows update and let me schedule it. Then restarted a couple times over an hour and it was done.
2. I love that the charms toolbar is gone with the need to use it for switching off my PC. Grr #annoyance. The new actions center replaces it but you don’t need it to SWITCH OFF YOUR PC!

3. I like the new start button with the exception that I liked the search bar from windows 7 inside the start menu. I do not want that in the task bar where there is limited space. If you click on start you can’t search for a program anymore. You have to click on that or the cortana icon(magnifying glass) if you choose not to use a microsoft account) in order to search.

4. Like Windows 8.1 it is fast at bootup and responsive while running.

5. Microsoft Edge is definitely the no frills browser to check out. Watch out chrome! DO try out the write on the web feature.

6. Cortana: This pretty much brings the mobile to the PC notifications, reminders et all. It seems gimmicky for a PC or laptop but might be useful in tablet mode

7. Multiple Desktops: WHAT?? Did you not notice this?? Its Task view pane..say Add desktop. This feature has been in Linux for a decade atleast. I believe in OS X as well although I must say I like the idea of the rotating screen in 3d from OS X for this.

8. So far, the apps that worked with Windows 8.1 all work with Windows 10. I have had issues with Norton working. The support says just uninstall and reinstall it but I have not had that kind of luck. So just uninstalled it and went to windows defender temporarily.

9 Use the Microsoft Upgrade Assistant if you think there are critical applications that you need once you upgrade especially from Windows 7 and earlier.