I think it's quite underrated as a musical capturing the angst buried underneath the surface calm of the characters making it one of the first truly adult musicals. And I love the Andre Previn/Comden and Green/Roger Edens score. The numbers are a tonic (Cyd's "Baby, You Knock Me Out" is quite appropriate as she's clearly a knockout here; Dolores Grey is a stitch in both of her numbers and as the two-faced smiling cobra of a TV star; the trash can lid dance and Kelly's "I Like Myself" couldn't be more entertaining).
But the truth is that the film was made under duress. The two directors were openly hostile to one another, Kelly was jealous of Michael Kidd and had his big showcase number "Jack and the Space Giants" axed from the movie, and with Roger Edens not present during its making, there was no calming presence presiding over the enterprise. Read the whole story in Hugh Fordin's terrific book about the Freed Unit. This film was a nightmare for all concerned, so the fact that I (and others) find it quite entertaining is something pretty remarkable.