Got this from the library recently for a niece of mine (yes it really was for my niece).
What you get really is Elite Beat Agents without the slick, slightly quirky presentation, character and "classic" tuneage. Its of course replaced by The High School Musical tunes, characters and scenes from the film and unlockables in the form of costumes awarded upon beating songs at certain levels.
The game mechanics are identical to Elite Beat, i.e. tap the circles in time to the tune although what I would say is that the game doesn't have the slickness or style that the above title has.
What is comes down to and this is probably the clincher is do your kids prefer "classics" (Madonna, Black Sabbath) over High School Musical tunes because in choosing between the two the likelihood is you would buy the one with the music that suits your/their tastes.
As a game taken on its own merits it ain't bad, I tend to compare it to EBA though and as such couldn't award it any more than 3 stars - originality isn't the games strong suit and it could have been visually better.