Even though I can get it for free (have a legal copy of 8.1), I will never buy or use Windows actively again. Ever since switching to Linux I've seen how far the OS has come; serious leaps and bounds have been made, and the majority of users can operate it with no loss of productivity and won't miss the expensive Windows equivalents, let alone the consistently shoddy performance.
Really, if you've never checked out Linux in depth, now is the time, before letting Windows screw you over yet again. "But if I can upgrade for free it must be worth it." No. No and no again. Try one of the versions of Linux that are beginner-friendly, such as Ubuntu or Mint. They're free, many versions are just as easy - or even easier than - Windows, and there is a free or open source version of almost everything. For gamers, Steam games are being added to the Linux list practically by the minute, and almost all non-Microsoft produced software has a Linux version now.
There's still a little way to go for it to actually compete with Windows, but it's growing exponentially and is absolutely worth looking into. Try it on a virtual machine if you're interested or unsure, and I guarantee you'll be impressed if you always thought Linux was just for tech-y computer nerds.
The reason I'm fighting so strongly for this is I feel a lot of people are pulled into the Windows gimmick because they feel like it's the only real option when that couldn't be further from the truth. "But isn't Linux not compatible with software X or game Y?" Possibly, and the likelihood grows by the day. But how many first versions of Windows are compatible with everything? There are major compatibility issues with every system until it garners enough users and support, and as long as people feed Microsoft out of complacency it will continue to give you a poorly performing, controlling, and limited environment because it can.
It doesn't have to be that way. You deserve better and with some effort and patience your computer can be your own. I refuse to let Microsoft (or to a lesser extent, Apple) tell me how my operating system should be run or make me feel like they're the only legit competitor out there.
All I'm saying is before you give in to Microsoft just because it's potentially a free product, try something new, and be open to the idea that this company doesn't have to dictate to you what you do with your computer.