I guess I understand the "can't remember a tune" complaint about Falstaff -- it's not that there aren't any, but rather that there are dozens, hundreds... but each lasts only a few measures, to be succeeded by another. Even the arias have a succession of melodic ideas. So nothing gets "plugged" in a way that assures we'll remember it. Repeated experience of the work helps with memorability, but not everyone will care to give it that.

I don't call it superior to those earlier masterpieces, but for me it's their equal; perfection, of a kind. It took me a much longer time to get the hang of Aida.