I did end up finally catching it last Thursday.
I wasn't really looking forward to it. I just caught it because it was free, and people kept telling me I should see it.
As I'm not terribly familiar with the music in the movie, nor do I have any real interest in the music in the movie, most of that didn't do anything for me.
But I do enjoy Jack Black.
And between him & the kids, it was worth watching. I didn't think it was "great" (maybe I woulda if the music did anything for me). But it was a little bit of fun anyways.
I say that if you actually want to see it, go for it. You'll probably enjoy it. I only felt it to be ok as I had no real desire to watch it based on previews.