First off, it's a musical, therefore it loses points right out the window instantly. Only a few musicals have ever been decent.
Second, it's about high school and once again, only a few movies about high school have been good and since high school is practically Satan's way of preparing you for the hell you will inevitably end up in for touching yourself every night, it therefore loses even more points on the title alone.
Third, it's about popular jock/preppy kids being likable/relatable characters. That has never happened in the history of forever.
Fourth, the main actor is a smug piece of shit closet homosexual and needs to die.
Fifth, it's boring. Nothing happens that has never happened in any other lame high school movie before it.
Sixth, predictable plot. who didn't see that coming.
Seventh, terrible singing. What's a musical with terrible singing? Just a terrible movie
Finally, it's loved by 13 year old girls with mild cases of down syndrome. It therefore sucks even harder.
That about do it for you?