Buried takes the experience of being buried alive and forces you to consume it. There are no flashbacks and no shots of the outside world - the camera never leaves the coffin.
Paul Conroy (Ryan Reynolds) is a truck driver who works in Iraq. His convoy is attacked by insurgents, he is buried in the coffin, and held for ransom. He doesn't have much: his anxiety medication, a Zippo, a pencil, some nut shells, and a cell phone at half battery life. He gains some other items later but it's clear he won't be able to MacGyver himself out.
Our experience with Paul begins as he wakes up in the box. The first minute is soundless black, gradually followed by panicked breathing. We quickly understand we're as trapped as Paul is. No matter how many varied camera angles or movements there are, you know you're stuck in that coffin for an hour and a half. But there's plenty of conflict in Buried, even action. The brilliance of shooting a film in a confined space is every problem is magnified.
Paul doesn't explain his situation well on the phone. He says he can't breathe. It's hot. There's not a lot of air. For Paul, these problems are urgent. For authority figures like the FBI, military, and his employers, these problems are secondary to information. As a result, Paul is treated like a hassle. There's a lot of potential commentary here about the way we interact with people on the phone, and how corporations and governments put themselves before individuals, but it's all about making Paul more alone.
Unfortunately being alone with Paul can get boring. Paul has to re-explain his situation to a lot of people. This is like good poetry when we feel exactly how the writer wants us to feel, but it's a horrible gamble. Jarhead made sure you felt as unsatisfied as its characters and that was a mistake. Fortunately Buried goes through emotions like a needle: up, down, up, down. So despite the occasional boredom, Buried largely succeeds in its design.
Ryan Reynolds isn't every director's first choice for this. Watching him in a coffin for an hour and a half is like staring at an itch. It seems like other actors would be much more effective dramatically, but would they create as much empathy? Reynolds's strength is he encourages us to laugh, which humanizes and helps us engage with Paul.