Just a tip but you might want to play around with box-shadow and find a good balance between translucently and busy wallpapers. Of course you cannot account for them but sometimes it's a good idea to just test a minimal and a busy one to find that balance.
As half-left hints at, strong transparency without blur looks good in screenshots on clean backgrounds but doesn't really work if you have a window open underneath the panel popups or a busy wallpaper. Try to open the menu on top of a browser window, it's a mess. In order to work the popup background need to be drawn from blurry semi-transparent "glass" image files.