Musicals have been a part of my life for a long time. When I was in elementary school, at a private Christian school (but that's a different story), we had a choir class. Ever year we had two music events, one for Christmas and one for Spring. We practiced for ages for both and we would get a break in between. For our break we would watch a musical in class, which would take several days. I remember watching Fiddler on the Roof and Sound of Music several times, I could probably sing all the songs from Sound of Music off the top of my head and it's one of the few musicals that I have absolutely no wish to see ever again as a result.
Too be honest, my two favorite musicals are two that I have only been exposed to in the last 5 years or so. The Phantom of the Opera and RENT are both relatively new musicals to be honest, though they have both had very successful and long runs on Broadway.
The Phantom of the Opera is one of the most disturbing musicals for me, simply because it very much causes me to root for the antagonist of the play. I fully believe that was Lord Webber's intent when he created the play, based off of Gaston Leroux's novel from the early 20th century. Like all of the play's created by Andrew Lloyd Webber this musical has exceptional music and and a wonderful story line that follows the plot of Leroux's book fairly well.
The Phantom, for all his faults, is a pitiable character. I get the feeling that he would have been a very different man, a genius of stable mind, if he had only been loved despite his deformities.
RENT is a story that simply a retelling of the Opera La Boheme. Despite that, the story is much more popular with many people. Of course I firmly believe it is because the story is so accessible to my generation. I think most of us can empathize with at least one of the characters in Jonathan Larson's "Rock Opera". The story is made all the more poignant by the fact that many of the people in the story are based off people that Larson knew. Larson died before his play could reach the level of popularity that it now has, his work lives on far past his own death.