This hastily assembled sequel to the blaxploitation hit Black Caesar downplays the gritty drama of that film to create a pure action tale with a comic book flavor. The story begins with badly wounded crimelord Tommy Gibbs (Fred Williamson) escaping an assassination attempt masterminded by corrupt District Attorney DiAngelo (Gerald Gordon) with the help of his estranged father, Papa Gibbs (Julius Harris). When DiAngelo's thugs attempt to kill him, Papa fights back and joins his son's criminal organization, a move that angers Gibb's top henchman Zach (Tony King). As Tommy and Papa build up their criminal empire, Zach secretly plots against them with DiAngelo. Zach also murders Helen (Gloria Hendry), Tommy's traitorous ex-wife, and pins in it on Papa to drive a wedge between them. Tommy gives up his New York crime operation and runs off to California. Papa takes over the operation, only to get killed by Zach during a fistfight. Angered by his father's death, Tommy returns to settle the score with Zach and DiAngelo. Hell up in Harlem delivers plenty of action set pieces and did fairly well at the box office, but lacks the consistency and the dramatic punch that made Black Caesar so memorable. As a result, it is considered to be one of Larry Cohen's lesser efforts.
~ Donald Guarisco, All Movie Guide