I took delivery of a 65 inch Q90T yesterday and have been using it all day. I was a little apprehensive about game mode from all the negative feedback about Samsung "gimping" game mode.
I have a PS4 pro hooked up with a HDMI 2.1 cable (for PS5) and I have to say game mode has exceeded my expectations. The image is clear, bright and the darks look great.
The darks aren't as good as movie mode and there is ever so slight bloom but you only see on loading screen and even then it's not bad. But during gameplay the Q90T is outstanding.
I tried game mode on firmware version 1304 and it was fine, played Call of Duty Modern Warfare, game motion plus on, all good. Nice punchy image. Didn't notice any dimming bug, blacks were good, HDR brilliant.
I upgraded to the latest version which is 1402 so I could compare. Again, same game and blacks have been improved and still retains the same punchy clear image. The only thing I noticed now was there was ghosting. So I turned game motion plus off and no more ghosting.
I tried a non HDR game, turned game motion plus back on and no ghosting so ghosting is only in HDR games with game motion plus on. I will make a separate thread to report this issue.
So for now I'm leaving game motion plus off. Why have it on anyway as it interpolates the image and increases input lag, so it's best being off anyway.