Yeah, you can't really be that surprised by that reaction from a bunch of high school and college kids. Being immature and making fun of stuff is just what they DO.
I have to admit I didn't think much of The Sound of Music when I was a kid either. It was just this corny black and white movie my parents used to love. And musicals in general seemed silly as hell to me.
It wasn't until my 30s (after being blown away by the Chicago movie) that I finally went back and discovered that "hey, this thing is really damn GOOD."