The Phantom of the Opera, musically speaking, is my favorite. I am not a fan of the dark spirit within it, but musically it pulls me in. There are funnier songs, better show numbers, but the mystery-feel of the music in Phantom is, by far, my favorite.
Related note, I like Cats for creativity. South Pacific, West Side Story, Singin in the Rain, and My Fair Lady intrigued me as a child.
I like how West Side Story is honest about prejudice and tries to bring real (or imagined) "sides" together.
Singin in the Rain is kind of cheesy, but I am grateful for how it depicts the changing landscape of cinematography.
Before the internet, My Fair Lady and Oliver Twist introduced me to the different parts of earlier British societies.
South Pacific snores at moments, but it looks at wartime relationships with a heavy dose of comedy interspersed, which I like.
Cannot forget Godspell, set in 1970s New York. If one ever wondered the role of John the Baptist, watch Godspell. He repeats it to where you will never forget. Hint: Prepare your ears
My major frustration with the imagery of Godspell is the final song and the main character's position. However, many people have been drawn to Christ (at least to remember what he's done) through this musical.
Here is the last part of Godspell, from a musical standpoint:
[video=youtube;4OjN13ovI9s]https://www.youtube.com/watch?v=4OjN13ovI9s[/video]