By definition a flop is merely a term referring to the economics of a show, if a certain show closes at a loss then it is considered a flop regardless of how many years it ran, how many stars were on it, the number of cast recordings it got, the brilliance of the piece, or whether it got great reviews or not.
Wonderful Town is a great, good old-fashioned fun musical, the revival boasted one of the best comedic performances I have seen when it starred the always-brilliant Donna Murphy, the score is a Bernstein gem with incredibly witty lyrics by the great late Betty Comdem and Adolph Green. Having said that, the revival closed on red therefore it is a flop.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"