We could just base it on what Brantley says and be done with it.
What a fascinating thread, though. I think the confusion is that you can't deem a work of art as good or bad as clearly that is a matter of opinion, BUT you can judge empirically TECHNICAL matters. I don't know enough about music to be able to do that, but I know enough about literature to be able to say that piece A is TECHNICALLY better plotted or has better character development. Same goes for a musical. I can say Sweeney Todd is a better defined character than Mr. Mistofolees because I know more about him and can point to specifics in the script that support that statement.
What I CAN'T say is that, empirically, Sweeney Todd is a good piece of musical theater while Cats is bad. I can say I enjoy it more. I can point to my reasons WHY I enjoy it more, but if my eighty five year old grandmother likes Cats more than Sweeney which revolts her (I'm making that up - she actually likes Sweeney), then for her Cats is a "BETTER" musical than Sweeney.
At most, I think we can argue merits of individual shows which may, in sum, lead one to say that one is on the whole better than another, but the terms "good" and "bad" are misleading.
Hi, Shirley Temple Pudding.