I won't say it's ruined, but I do think that the advent of the megamusical (Phantom, Miss Saigon, Sunset Blvd, etc.) left a very bad taste in my mouth. I'm not fond of movies made from musicals, although The Full Monty, Hairspray, Dirty Rotten Scoundrels and The Wedding Singer surprised me. I'm not thrilled by shows that have worn out their welcome, partly because those same shows keep touring and being produced by community theatres, so we're overexposed to them out here in the midwest.
If we want to see movie musicals, we need to get them from Netflix. The idea of a helicopter landing onstage, a house going up in the air, or a chandelier crashing onto the stage doesn't make me want to see the show (although I did see Sunset Blvd., and the staging proves it belongs on the screen.)
I also think Cameron MacIntosh and Andrew Lloyd Webber are responsible for misrepresenting the musical theatre. It's sad that a good play, even a revival, has to struggle, while musicals open and play and play and play.
This was an interesting link. It won't keep me from going to NYC and seeing more shows, but I'm far more selective about who gets my money than I would have even 25 years ago.
NYC Visitor and Broadway Fan