Pirates of Penzance is easier to take because it doesn't take any time out to be "artsy" like Singin' in the Rain or a hundred others do. When it is artsy, it's purely satire, at least in my favorite version (starring Kevin Kline, Linda Ronstadt, and Angela Landsbury), where they make references to Elvis and some other pop by using echoes and such. when Mabel does her major virtuoso solo, Fredrick is getting frustrated because he's trying to kiss her. Every time she pauses, he leans in, but then she starts.
Now: there IS artsy stuff. Kevin Kline does some amazing dance stuff, as do the policemen, but it's FUNNY. More like Danny Kaye than Fred Astaire.
Anyway, I think that Guys and Dolls is a passable musical, but that's partially because I saw it with my wife at the Kennedy Center. And I enjoyed Les Mis, though the novel (especially if you can cut out 50 page descriptions of the layout of the Battle of Waterloo and the whole sewer/bowels metaphor) was far superior.
I don't hate musicals as much as I sound like I do. It's just really easy to mock Fell that he is "out of the closet" about his musical liking.
But if he doesn't like musicals, it may just be a macho thing, and you may never get him over it.