The glossy layer applied to the album art is probably intended to jazz it up and make it look like a shiny plastic-wrapped CD. However, it just gets in the way. My eyes aren't very good, so I have to constantly hover over the art to get the "real" version. It'd be nice if the gloss was removed, since it's just not needed. It makes it very hard to see anything, much less details.
Also, since moving to the Imaging library, left-clicking the art no longer activates the larger pop-up version. I'm forced to hover over it for a few seconds before the popup activates. It'd be nice if the click functionality was restored. Imaging also seems to have much poorer scaling than older Decibel versions that didn't use it. With Imaging, I notice many more visual artifacts in album art: ghosting, banding, etc.
The gloss effect can now be disabled by using the --no-glossy-cover command line option.
As for the click option, it requires hacks in the code to correctly handle enter/leave events, that's why it was removed. Current timeout for displaying the cover is 600ms, which is not "a few seconds" :-)