5.9: The screen looks bad
When using 5.9 on the phone, the internal screen looks... bad. I'm aware it's not a really descriptive term, but I'm not sure how to describe the difference, as it's pretty subtle. It's the most noticeable when in motion, like when sliding the lockscreen. It feels kinda like subpixel rendering going wrong? Slightly pixelated, but only sometimes? The default wallpaper also looks a bit brighter, with some kind of very subtle vertical stripes on it.
Booting into 5.9 makes the screen consistently look that way for me, while booting into 5.7 makes it good again.