How bad is it? It's one of the worst star-vehicles. It wouldn't even make a good music video.
Should you see it? No.
Back when Mariah Carey could sing (she seems to have given up with the advent of Autotune), someone thought she could carry a film and she thought she could act. It's the standard story of a girl from a difficult background overcoming obstacles and becoming a star. Though Terrence Howard, Eric Benet and Ann Magnuson are in it, their acting doesn't make up for the terrible non-acting of Carey. For some reason, Padma Lakshmi is in this. None of the songs are memorable, nor are the performances of them. There's also a number of odd plot problems: everyone instantly knows when she gets a contract without being told, her demo gets played by a DJ without his listening to it first, her concert song about her murdered boyfriend is way too cheery and in the end her relationship with her mother is miraculously better.