I've upgraded to Windows 10 and it looks awesome!
Tested only Microsoft Edge yet, and it looks much better than Google Chrome in my opinion.
Haven't tested yet any game but i'll do it later. About the Anti-Virus i'm not a big fan of Windows Defender so i've disabled it in Windows 8.1 and it looks that it wasn't activated in Windows 10. I use ESET Smart Security 8 as Anti-Virus.
Windows 10 looks really great, i had a problem at start with my resolution but the display driver was outdated and a update solved the problem.