How about "Little Shop of Horrors?" Compact, funny, suspenseful--keeps a tongue-in-cheek tone throughout while still making you care about the characters.
Anyone want to start a "worst book of all time" thread? I'm not talking about obvious flops ("Legs Diamond") or jukebox semi-revues ("Good Vibrations"). I'm thinking of musicals that were hits in spite of their dreadful books. My own submissions:
Sweet Charity
Bye, Bye Birdie
The Sound of Music (stage version!)
Camelot
Saturday Night Fever (I know it wasn't a "hit", but it's so dreadful it deserves a mention)
Footloose
Fame
Starmites
I ask in all honesty/What would life be?/Without a song and a dance, what are we?/So I say "Thank you for the music/For giving it to me."