I have been using 10 since the 1st beta - I have not had any issue with my games. PS2, Tomb Raider, MGS Ground Zeroes, The Witcher 3, ARMA 3. Of course that doesn't mean you wont see any issues because you may have different hardware, my guess is that you won't see an issue. Only slight issue I have had is that the Creative XFi has a slight install issue that can be quite easily resolved.
Windows 10 really seems to have no issues with games or program compatibility. Drivers on the other hand, is another story, Nvidia seems to be the worst right now.
There is now like a dozen threads about PS2 and Win 10 by now. I think we should focus on one of them.
my fps gradually increased from 30 to 50 with an intel hd graphics 2500 from core i3-3210 and 4gb ram. that's so cool in windows 10. Win 10 is very good optimized for games and the support for dx12 just rocks.
It could be maybe some improvements in multithreading and memory management. There are also improvements like this in the transition from 7 to 8.