High School Musical is very much an up-beat childrens/teenage musical, and is very typical of a shiny, happy Disney film. In fact, it is a little too up-beat for my taste.
For a musical, I don't think the musical numbers were particularly strong, and there weren't that many of them compared to spoken narrative. The songs didn't always seem to fit properly and the voices on the characters didn't sound too natural. I don't know if the actors did their own singing or not but it sounded too studio-like for my tastes.
I can only remember laughing at two very small parts. The jokes (if that's what they were supposed to be) were not very good.
I don't really see why so many people like it, but each to their own. In my honest opinion it was altogether too cutesy and perfect a film for me to like.