iTunes 12 introduced a new screen when you click "Get Info" that’s far simpler than it used to be. Gone is the place to drag and drop artwork, grouping info, and more. Thankfully, TUAW points out you can get that old screen back with an Option-click.
All you need to do is select a track (or group of tracks), right-click them, then Option-click the Get Info menu. This loads up the old edit menu where you can once again drag-and-drop album artwork, easily create special sorting sections, and everything else.