John Rambo, as the title sequence called this movie, is indeed a movie that finally completely proves how violence can be used to preach anti-violence. This movie has such realistic gore, without ever glorifying it, that I had to convince myself while watching it that it is just a movie. Rambo's insanely calm and cold-blooded demeanor while he massacres an entire infantry is reminiscent of how killing so many people has killed him of human emotions.
Sly Stallone is indeed a good writer; a better writer than a director. The movie makes no pretense in sophisticated urbanism. It plays out exactly and as simple as expected from Rambo's POV. This man lives only because he is alive, without ever forgetting what he really is. His mundane life is interrupted and eventually unhinged due to a simple decision - to help others, and only because he can rather than he should. The movie is equally linear in its plot and telling, yet leaves an impact as powerful as after a Saving Private Ryan.
In First Blood and the two sequels, John Rambo has fought bigger battles and faced situations of a lot more peril. He has run away from 'what' he is, or accepted and despised his self. But here, with age and the maturity it brings, he finally comes to peace with 'who' he is. And that is where as a personal story, this scores well over the first three movies.
Like for all muscle-men, Stallone's physique has taken away any recognition he deserves for the mind he has. Multiple Razzies and stereotypical roles has him always judged as a bigger better version of Van Damme. But with a lot more creative control and less media focus, he is finally able to continue what he started of as a nobody in the first Rocky.
Overall this may not the best Rambo movie (First Blood still takes that cake), but it surely is the most effective one.