Rates 6.9 on IMDb (21,556 votes) and 56 Metascore, so it's viewed as a high-average movie. (5-5.7 is low average; 5.8-6.4 is average average; 6.5-6.9 is high-average.)
Critics seem to want a consistent kind of genre or tone, and this movie doesn't have it in their eyes; so they tended to be critical while finding some things praiseworthy. However, it presents a consistently dark view of human nature.
My opinion is that if they were familiar with neo-noir as a category or place-holder, which most reviews seem to miss, they wouldn't have this criticism problem. They'd see the black humor, the violence, the corruption meshing together along with dark photography. Furthermore, they wouldn't worry so much about the movie going against the prevalent gung-ho mentality of WAR around 2001. The military is indeed a vast pit of corruption and waste and misdirected resources. The Pentagon accounting system routinely loses billions and can't even keep track of men and materiel.
The director knew this, saying
“I think it’s actually surprisingly close [to reality]. I started doing some research into it when I was writing the script and I’ve got documents which show things like murder rates on US Army bases—there were between 25 and 30 murders a year. And things like accidental deaths—there was between two and three a day. And suicide rates...
“There’s also statistics about how many weapons just went missing during the course of the Cold War. Billions of dollars worth of weapons just disappeared. And drug use—the army in the end had to introduce drug testing to try and stamp it out. If anything, what is depicted in the film is toned down from reality. What really happened was much, much worse”.
Let's not forget either that the military is home to oodles of sexual assaults, not depicted in this movie, competitive with Hollywoodland's disgraces. There is instead a reverse racist assault, black on white, in this movie.
Ed Harris, Scott Glenn, Joaquin Phoenix, and Anna Paquin all do a good job bringing this to life. Supporting cast works well too.