I always thought a good Rambo sequel would be a movie with no real plot or dialogue (so not really that different than any other Rambo sequel).
The movie opens up with Rambo waking up in some humid jungle hut. He looks hungover and already pissed off. The only dialogue in the entire film is Rambo casually uttering a "God damnit" as he rolls out of bed to grab a machine gun. He then starts laying waste to thousands upon thousands of Vietnamese for the next 90 minutes for no explained reason. Men, women, children, dogs, infants still in the crib, infants still in the womb, elephants, jungle cats, etc. The movie ends with Rambo wrapping himself up in an American flag and falling back to sleep to the sounds of soft weeping and the death throes of his victims.