I have installed "OMG the best version of Windows yet," aka Windows 10.
It is quite rough around the edges.
My desktop (with Japanese language pack installed):
Live tiles are often not "live", they are static and do not update. Live tiles also have issues with languages (if you switch languages they can appear as the wrong one). Web search is also limited to Bing, it would be better if Google was an option.
Japanese fonts issue:
Windows 10 uses new fonts for Japanese and its garbage. If you don't have a really high resolution screen, they can look blurry or pixellated, as in the screenshot of Chrome above.
Input method editor changer:
There is an issue where you can't use Japanese input as default if you do not use Japanese as the display language. You could do this in previous Windows - eg you could have English version of Windows and have Japanese as the default input language.
Windows recommends using a PIN to log in, yet the Numlock key is ALWAYS disabled on the lock screen (FUUUUUU). The Mail app is garbage: if you have more than one email account it sucks bad. The Calendar app also needs more work. Some apps don't work well in Windows 10 (eg the MEGA app I use to sync files). Some settings DO NOT get saved when you change them. Many Windows apps crashes (yes, even the Settings app) at random.
Unless you're curious, stay with Windows 7 (or 8) until issues are worked out. It's not that big of a leap, really.