“Kickboxer 4” barely resembles its predecessors. It's edgier, meaner- yet oddly, sillier- and takes David Sloan down a relatively dark path. It's still not as good as “Kickboxer”, but it's better than the other two sequels.
Make no mistake, "The Big Boss" is NOT a good movie. But the badness, mixed with the weirdness, creates an eccentric atmosphere that I personally found appealing. Yet more importantly, it's weaknesses contributed to Bruce Lee's strengths, enhancing his effectiveness.