First you have to disabuse yourself of ever being able to justify this movie's premise: No one goes off and murders everyone they know after killing a taxi driver in a moment of road rage. But if they did...
You'd have this movie, a pseudopsychological study of compulsion and guilt.
The guy works in a slaughterhouse where he conveniently disposes of them, only, in a stroke of poetic justice, to have them turn up back on his dinner plate. Hence Cannibal Man.
Vicente Parra must have been a hunk of his time, as he appears shirtless as often as dressed,.and he develops a relationship with homoerotic undertones, initiated by a stalker-cum-confidant who watches him with binoculars from his elegant high-rise apartment thru the skylight in the mass-murderer's hovel below.
The film screams '70s in style and the use of camera gimmicks not seen since
Overall not bad, if you can suspend your disbelief.