Surprisingly, I played a few rounds of Rainbow Six Siege and PUBG PC on Windows 11. It felt surprisingly smooth... Didn't really feel like it is a Beta release.
So far there are a couple of (minor) bad things I wanted to point out:
Fluent UI Transparency effects can only be observed on the primary monitor (for now, hope they'll fix it) (UPDATE: Only observed on the new Windows 11 apps so far that use the transparency effect, not any of the old ones that haven't been updated from Windows 10)
Sometimes, File Explorer reverts back to the Old Ribbon UI...