As Hollywood slowly eases us out of awefulsome August and into mediocresome September, Righteous Kill, the long-awaited first-ever movie in which Robert De Niro and Al Pacino share significant screen time, finally lands in theaters. But while most critics are understandably focusing on the topliners ("There's no getting around the fact that the erstwhile young lions are long in the tooth," raves the L.A. Times), what we want to know is this: How is 50 Cent's — excuse us, Curtis Jackson's — performance?