Interesting topic (which, of course, I missed the first time around
).
I have found very often MUSICALS are MUCH better than the books upon which they are based - Have you ever read the book behind the "Sound of Music"? Or "State Fair" or "Carousel"? Don't bother! (Except the Story of the Trapp Family Singers IS interesting from a historical point of view!) The list can go on ad infinitum - though, of course, there are exceptions. (As an aside, did you know that Maria Von Trapp's granddaughter is a singer-songwriter? Lovely voice, not enough expression for my taste - one song at a time is fine.)
Mary Poppins is a wonderful group of books - DIFFERENT than Disney's interpretation, but both stand on their own beautifully.
My Fair Lady is the perfect adaptation of G.Bernard Shaw's Pygmalion - of course, when you combine a great play with a great composer you should get a great show!
Most of the time I prefer the books...