The most wonderful non-hit I ever saw was Baby.
From that first duet, with Todd Graff and Liz Callaway considering what their baby might be like, I was in absolute ecstasy. The female trio, I Want It All, was so wonderful, I thought "Wow. It can't get better than this." But of course Liz' rendition of The Story Goes On was the most thrilling performance of a new song I've ever seen on stage. And the love songs: I think I Chose Right is the best love song to hit Broadway since the 1970's; And What If We Had Loved Like That fills me with such emotion, I can't speak of it.
If I go into the reasons I think it wasn't a hit, I'd be going in to some very controversial topics, so I'll just say that, among singers I know, the songs from Baby are performed more often than any other show of the past two decades. In that sense, it's a hit - it's never been forgotten.
Now, speaking of forgotten...