Update 8/7/14 #1: Quite a few of you experienced issues with album art after updating to version 5.6.1616P. Google has now released a new update 5.6.1617P which resolves this (you can find the new APK below). You may need to clear data and restart the app if album art still doesn't show up.
Update 8/7/14 #2: Google posted the official changelog, and looks like this is also new in this release: "You can now undo tracks removed from playlists and the queue via swipe."
Google has been playing around with the Play Music interface a bit lately, but the widget hasn't been keeping pace.