I can't completely explain why I give this five stars after giving the first two sets four stars each. This is just the way the opera, in particular, strikes me. I'm no great opera fan, and to my knowledge, America just has not yet proved itself in the operatic field although it's tried. It will take time, but I do see Copland's work as someday being considered the best example of American opera. This is all subjective opinion, obviously, and I'm sure there are those more knowledgeable who will disagree. So be it.
All in all, these three sets will give you a complete overview of one of America's most important composers.