I have to agree that these are some of opera's greatest moments in the later part of the 20th century. The Pearl Fishers Duet (Au Fond du Temple Saint) sung by Jussi Björling, Robert Merrill is a big favorite of mine. Monserrat Caballe sings La Boheme here, and I couldn't believe my ears; maybe the best version of this I've ever listened to.
I like these assortments of opera arias for the variety, for having all my favorites on one CD, and for the great performances you can find sometimes, like Caballe's here.