Often when Merrily is revived, the same doubts get expressed - "it never really works", "the lead isn't likeable" - but then audiences see it and come out pondering their life choices.
It works at the deepest level. The authorial skill on hand is the reason. It may be the one Sondheim musical that is still performed two hundred years from now, because the struggle between idealism and compromise is inherent in our human species.
And I speak as someone who loves Pacific Overtures, Sweeney Todd, and so many others with a passion. And even Passion.