The brand of humor in Charlie Hebdo is very particular, and somewhat unique to France. It is absurdist (in the tradition of Rubrique-à-Brac), a type of humor comparable to MAD magazine and Viz in terms of anglo-saxon publications. It is also extremely satirical, comparable to The Onion and The Colbert Report, e.g. saying Charlie Hebdo is homophobic is as absurd as saying Stephen Colbert is right-wing, or that Ali-G is racist. Charlie Hebdo humour is often crass and shows a complete lack of respect for many institutions, à la South Park. More explanations of this are offered in this article from The New Yorker and this article in Mediapart.