A former gang member, now an undercover cop, travels through a dangerous inner-city labyrinth to kill a notorious gang leader. Boyz n the Hood meets Apocalypse Now.

Yes, I agree with Anonymous. The comparison to other movies (with the goal of describing what genre(s) it fits and its marketability) belong in your pitch or treatment, not the logline. If you can give us a quick clue as to why your protagonist wants/needs to kill this person that would help, too. Sounds interesting, though!

I've always heard that naming other movies is the mark of a hack or amateur. I would take that out if I were you.

Apocalypse Now is, I believe, losely based on the novel Heart of Darkness by Joseph Conrad.

Seems like it needs more. What makes this story unique? What makes it stand out from every other crime drama with gang members turned cops? A former gang member chasing a gang leader is interesting but it needs to be more of a hook. Maybe the notorious gang leader was the undercover cops mentor...see how that situation would make it more complicated and give it more of a hook? Its good as it is...just could use a little more.