I usually do not review performances together even when they are part of the same film unless reviewing one performance naturally causes me to mention the other constantly and this is the cause of Dafoe and Berenger. As the two men portray the beacons of morality within the film Berenger's Barnes representing evil well Dafoe's Elias represents the good. With Oliver Stone an actor must be careful when Stone's heavy handed black and white writing and direction is around, since it can easily lead to very over the top performance, luckily though Berenger and Dafoe are competent enough not to be swept up into the over the topness Stone can often cause in performances.
Neither of the actors overplay their part and both do attempt to turn them into real people, even if Stone's writing tries to keep them both a little simpler than they really needed to be to even convey his theme he wanted out of the two of them. Berenger as the bad Sergeant is the rougher of the two scarred from the war, but also dominate over the the men even over their lieutenant. Berenger early in the film is effective because he does not try to be the eventual point of Stone's early but rather just shows a tough Sergeant leading his men along and doing his job the way he sees he must do it. Dafoe actually counters him in much the same way he doesn't try to make Elias a man of good, but as well just a Sergeant doing his job although in a kinder more humane fashion and interestingly enough early on their differences don't seem that extreme.
The two show two very different fashions in which the two Sergeants cope with the war but both actors handle it effectively so. Berenger shows Barnes to basically internalize most of his feelings toward the war and only seems to realize it in his acts of violence. Although Berenger is great in a few short moments where he shows the emotions quietly coming out of Barnes over the death of soldiers that is very well handled considering such a moment could have been completely forgotten with the path his character eventually takes. Dafoe on the other hand more of show an exasperation in Elias over his years in the war finding them tiring him, and losing faith in the effort. Dafoe conveys this carefully because he does not show it as if Elias has given up but rather there is a still a passion to keep his men alive, but still he sees much of his efforts being futile.
There paths though converge quickly as Barnes murders civilians and Elias fights with Barnes because of this. The two performances than assume their roles of the good and the evil. Berenger is appropriately intense and chilling as Barnes when he goes over the edge and starts killing. He acts though not quite as some sort of soulless villain but rather a man who has just gone over the edge. Berenger does not turn Barnes into the most memorable of villains but that really is not a problem as Berenger plays down his evil enough to be far more realistic as Barnes actually. Dafoe as well does not overdo the goodness of the character for a moment. Elias simply is just a good man effortlessly so because of Dafoe. There is no visible effort in his performance to portray the kindness in Elias he is just honestly a good man.
Both actors achieve in developing the central conflict of the film without hammering it in as much as lesser actors would have even though there director probably would not have minded either way. Just as if not more importantly though both are effective in making their characters human beings first before being representatives of dark and the lighter side of mankind. There performances are strong efforts throughout and each have individual moments that do stand out. Dafoe of course has his big dramatic final scenes which is terrifically acted by him. Berenger best moment comes in his moment we he challenges all of Elias' men on their death threats toward. Berenger is great in the way he absolutely controls the moment and the men as Barnes. Both give strong performances that serve their film probably as well as they possibly could.