I also think Full Metal Jacket is overrated. It does have one of the best first halves of any movie ever, but once boot camp ends the movie is pure average sauce. And ugh, Matthew Modine sucks. One of the worst actors of all time.
I even love the second-half of FMJ. The sniper scene, in itself, is amazing, and Joker excecuting the Vietnamese markswoman is one of the most heart wrenching scenes in film history.
But the thing is -- the First-Half and Second-Half of FMJ is much more intimately connected than people give it credit for. Thematically they link like gloves. The boot-camp is a basically brain-washing center. The recruits are stripped of their identity and made into bloodthirsty, sexually perverted grunts. The Drill-Sergant specifically picks sexually loaded insults and orders to galvanize them towards this depraved mindset. A ton of the insults he throws at them is aimed at making them connect sex with violence ("this is my rifle, this is my gun", for example. And they are even ordered to give their rifle a female name... and then sleep with them!).
The second-half is basically all about depicting the results of this training. It's no suprise that Joker is the only humane, sensitive soldier in the field who does not commit some sort of atrocity or undignified deed. He is the only one who survived the brainwashing. Everyone else is a psycho to some degree that has no moral qualms about shooting civilians, abusing prostitutes, or taking joy in killing their enemy. (The infantryman that shoots the sniper for example, humps his hips back-and-forth in the air right after having nailed her, as if fucking her).
Yet, in the end, when Joker is coerced into killing the female sniper (or as Animal Mother says, "fuck her") he too losses his inner humanity, he gets the "1000-yards stare" and becomes as emotionally hollow as his fellow grunts. In the ending scene, he marches in perfect alignement with his fellow troops, whistling the mickey-mouse tune alongsides them, signifying that he has become just like them. If you recall, the Drill-Sergent asked Privete Pyle in that pivotal scene when they where in the bathroom if he had gone completely "Mickey-Mouse"?, ie: if he had gone crazy? Joker went crazy in the end. That's great storytelling.
