A small gripe, but it's a bit irritating:

If you play Fullscreen, the game can be minimized but it won't "tidy up" -- reset brightness, etc. Also, getting back into the game sometimes causes a crash.

If you play in windowed mode, the game won't crash, but it also won't minimize. You can Alt-Tab to other open windows, but there's no way to get to your desktop, which I often want to do. I have to entirely quit the game to get there.

As I say, a small gripe, but most professional games are a bit more well-behaved than this these days.