There is a pop-up "tooltip window" that displays for approximately 5 seconds when you mouse-over the thumbnail images in the "View as Thumbnails" display.  It currently shows: Title, Rating, RunTime, Production Year, Release Date, Purchase Date, and Genre(s) for the thumbnail you are on.

I would like to see this become a customizable list of details that display.  (from the "Thumbnail Display Options panel...?)

..would like to be able to add Last Watched Date to this, but suspect others will have different details they would like to see in this pop-up.