Keep in mind that you can still upgrade to Windows 10 but you will have to pay the full cost.
Windows 10 is a dramatic improvement over Windows 8. The new OS not only looks nice, the desktop software is intended to seamlessly integrate with tablet apps. CNN’s review of Windows 10 provides a quick snapshot of what’s new in Windows 10. As well, with the upcoming consumer release of the first service pack for the operating system it may be a good time to reconsider upgrading. On top of that, Microsoft will eventually stop issuing security patches for Windows 7 and 8, so you’re going to want to upgrade someday anyway.
If your PC is not powerful enough for Windows 10, don’t upgrade. However for everyone else now is the time to upgrade to Windows 10.