Full Metal Jacket is not one of the best Vietnam films but it is a commendably ambitious production.
The first part, dealing with the bastardisation of new conscripts is memorable, particularly for the performance of Lee Ermey as the Drill Sergeant (a role which Ermey had performed in real life) with Kubrick well in command of his means. The second part of the film, supposedly set in Vietnam, suffers from a lack of focus and problems of authenticity, particularly when compared to films such as Apocalypse Now and Platoon, the latter of which came out only the previous year. Shot in the grounds of a disused power station in London, tricked out with a bit of signage and a few sickly palm trees, it never convinces as the real deal, although Kubrick's staging of the climactic battle scene is impressive.
Matthew Modine, a youthfully slight and anonymously mild-mannered individual (somewhat reminiscent of Keir Dullea, indicating perhaps Kubrick's fondness for a particular type of principal character), whose film career never really developed after this, gives an understated performance but it is one that only adds to the anonymity of his character and the result is dramatically underwhelming.
FYI: Kubrick's daughter, Vivian, did the original score under the name Abigail Mead.