This got a 35% on Rotten Tomatoes, but I feel it fully deserves five stars from me. It's a tense war picture more than a scifi movie, capturing the experience of what it's like to be a Marine in constant, heavy combat. The characters are well-drawn and relatable. I am guessing they had a lot of actual Marine advisers, bringing plausible realism to the battle scenarios. To this civilian (and I may be completely wrong), it rings very true to what combat must be like --- you get a good peep at the professional standards and practices of soldiering.
I'm frankly stunned so many critics hated it when far stupider action flicks (e.g., Thor) get rave reviews. Part of the criticism of the picture comes from "stupid dialog", but I honestly found the things people said not "stupid dialog" but an attempt to capture the way people really talk. I mean, if you're in a war situation where you're trying to comfort a little boy who has just lost his father, you are not going to be spouting Shakespeare, and you're inevitably not going to say all the right things you might say if you had time to reflect. That's the case with the dialog here.
As someone who is ignorant of military life, I found the teamwork very interesting to watch, and it seemed plausible to me, like it was the way Marines in such a situation who were competent soldiers would really interact. Now, again, I say this as someone who has never been a Marine or even known a Marine, so I may be completely wrong, and, if I am, leave a comment telling me how this movie gets it wrong. I'd be interested.
I liked the little detail of the "Retreat, Hell" chant, too. It was inspiring, but not too corny. It was sympathetic how they used the chant to buck up their courage and get focused back on task.
The effects in the movie are more subtly done than a lot of CGI. It doesn't *look* like CGI in most scenes. There are not the annoyingly dark filters a lot of such movies place over the image to hide any defects in the computer work, so it has a kind of gritty realism.
One criticism I have is of the shaky camera work. I understand that this is an attempt to add to the realism, but I find it a cheap trick. The choreography of the scene should communicate the chaos and desperation, not the cameraman!