Gaming is fine, I haven’t noticed any issues but I have to admit that I’m a casual gamer at most. The monitor supports FreeSync and refresh rates up to 165Hz.
I haven’t compared VA to OLED yet, but the latter costs at least twice as much where I live. For me personally, I don’t think that’s worth it. My previous monitor was a Samsung CF791 with Quantum-Dot but honestly I find the iiyama to have nicer colors. That’s highly subjective of course and the CF791 was released roughly 10 years ago, so take this with a grain of salt.