My only opinion on the overlay effect is that if it looked the way it does in KissCool's third image - the shadow on the font - I might actually use it. (Added: I also observed the awkward overlays as shown in KissCool's most recent post, when I checked it out just now.)
I'm REALLY happy to have the auto-hide for player bar, thanks! I only wish that the MusicBee button and window buttons were full opacity, since they hide so quickly now. It looks weird when they should be the same color as the player bar and aren't.
My main concern at the moment is images like this.

I'm not sure I entirely understood the changes to background fill, but I'm perfectly happy with the single-color background.
This looks really weird, though. Shouldn't the photo at least be scaled to the full window? I see others that are displaying correctly with the image behind the track info, but only when they fill the whole window. I assume it's intended, but it seems inconsistent, and with a *compact* player to begin with, I don't want the images scaled down more than necessary.