Windows 10 is out for technical review by anyone desiring to do so. Simply go to Microsoft’s site and look for the trial program, and sign up to get an ISO that will install Windows 10 with a trial license. I would strongly recommend to not wipe your existing OS to evaluate this, and instead create a VirtualBox VM and install to that. VirtualBox is a produce from Oracle which is free for use, and allows you to virtualize a PC to run another OS from within your current OS.
So far I can say it looks promising. The desktop is back to being the center of the OS, and the start menu is back completely. It looks like Windows 10 is a nice shift back to focusing on the things you need in a desktop OS, instead of trying to change your desktop into a big tablet.
Microsoft is famous for following a pattern of “great operating system” followed by a flop, and then “great operating system”. Windows 8 is to windows 7 what Vista was to Windows XP. Hopefully those that purchased Windows 8 will get a free or very low cost upgrade.