I'm going to be really horrible and just c/p the HSM specific excerpts out of this Vanity Fair article, but the whole thing (about the evolution and reception of song-and-dance entertainment in recent times) is very interesting. I don't agree with some of their points, but still worth a read if you want to click over to the source.
Vanity Fair Excerpts, 'Of Glee I Sing'
But three years after the release of Camp, the cornfield re-sprouted shiny and new. Pairing the most can-do romantic couple since Mickey Rooney and Judy Garland struck up the band for MGM, Disney dropped a duo of adorable kittens named Zac Efron and Vanessa Hudgens into the twitchy laps of America’s teens and tweens in an original TV movie called High School Musical (2006), and a new Romeo and Juliet were born, only without all the dying at the end. It was an instant phenomenon and a heartthrob juggernaut. The propulsive popularity of High School Musical begat High School Musical 2, which begat High School Musical 3: Senior Year (or, as I think of them, The Trilogy). High School Musical set the menu for Glee in many ways, from its ongoing tug-of-war between the royal order of the jockstrap (the varsity squad) and the roar of the greasepaint (the class revue) to its gay-friendliness: its rejection of the bullying notion that singing and dancing are strictly for girlie boys and the chicks who dig them, and that being “different” is some kind of social disease. It’s what’s inside that counts, not the purple eye shadow and roguish ascot.
So what novel elements has Glee injected into the H.S.M. formula that have propelled it above and beyond?
First: in previous coming-of-age sagas, the adults trying to thwart sudden outbreaks of choreography were portrayed mostly as sincerely mistaken, behind-the-curve fuddy-duds. They weren’t evil, just unevolved. Glee’s genius coup is to give us a villain figure of seething hostility and cunning antagonism... [Stuff about Sue]...
Second: unlike High School Musical (which churned out pop-y original tunes and caramel ballads) or the ill-fated remake of Fame, Glee doesn’t slavishly court a single demographic. It spreads itself across the quadrant by employing an ecumenical songbook that exerts a multi-generational attraction. And Glee respects its borrowed offerings: it doesn’t give them the bum’s rush or practice artistic coitus interruptus... [Stuff about songs and performances]...
The unhappy irony is that, while Glee is hitting the heights, school arts funding is being slashed across the country due to the steep recession and declining tax revenues. To the bottom-line mentalities that make policy, the arts are still considered frilly extras, a myopic view that—oh, forget it. I don’t want to end this column on a downer. Five minutes ago, I was feeling so cheerful, and then I had to go introduce the real world into the discussion, like an idiot. Better I should go on singing in the rain, the way God and Gene Kelly and MGM intended.