“The Massacre,” the latest CD by Curtis “50 Cent” Jackson, is good, but not as good as his debut album, “Get Rich or Die Tryin,’” which was released in 2003 and sold more than 11 million copies and is being investigated for copyright infringement. 50 Cent’s group, G-Unit, is back, but with more members: Spider Loc, Mobb Deep, M.O.P. and Olivia, the only female and also only R&B singer. The rapper The Game is on “The Massacre,” too, but he has since left G-Unit. The bigger band makes a bigger sound.