I found a couple that used posters with marketing copy and actor names on them and those I definitely think are crap - and changed them; others were mostly just preference on if considered good or bad posters.
Since the UI\UX for watched status changed I’ve been picking posters with titles at the bottom or middle more often so that the titles aren’t covered by that annoying box\green check overlay as well.
All the posters seemed to be good image quality though so I thought that was a benefit.
None of the posters I had set manually changed and that was my only big concern.
I did notice that if it’s using a “new” default poster, that in the UI of selecting a poster it’s not the first one in the list anymore. In the past, the first one in the list\display was the default so that threw me off a bit seeing the selected poster in the middle or end of the list.
Overall I only had to “adjust” about 10 posters out of ~1000.
Edit: It might be nice to have a guide or pre-built form to report bad posters for specific reasons that Plex would consider reasonable; wrong poster, marketing copy, bad resolution, etc
