It's difficult to hold the interest of an audience for almost three hours, especially in an age where people can't go five minutes without checking their text messages or tweeting about what's happening in a movie. Heat was made in 1995 when it was much easier to forget the outside world for three hours, and that's part of its strength.
The most obvious thing to mention is that Al Pacino and Robert De Niro appear on screen together for the first time, and it's the first time they two have appeared in the same film since The Godfather: Part II. Both actors are close to their best and their two meetings are memorable.
Lt. Vincent Hanna (Pacino) works for the LAPD. His job is his passion and he places it above personal relationships. He's on his third marriage and that is failing because he only gives his wife a fraction of his attention if he's home at all. Neil McCauley (De Niro) also has a passion, but he's on the wrong side of the law. He heads a group of thieves who are professional and extremely effective. Unlike Hanna, McCauley doesn't want any personal ties preventing him from being the best he can be.
McCauley has a favorite quote:
"Have no attachments. Allow nothing to be in your life that you cannot walk out on in 30 seconds flat if you spot the heat around the corner."
The movie shows us how effective McCauley's crew is when they rob an armored truck early in the movie. One of the crew, Waingro (Kevin Gage), is a loose cannon. His behavior leads to three unnecessary deaths so McCauley decides to kill him. Unfortunately, a passing patrol car distracts McCauley and allows Waingro to escape. He's a constant source of trouble for the remainder of the story.
McCauley's life changes when he meets Eady (Amy Brenneman). Instead of being a free agent, he's in danger of becoming tied down to a relationship. Will he abandon the idea that he can walk away from any situation in 30 seconds, or will she complicate things?
What sets Heat apart is the strong characterization. Mann takes his time establishing all of the characters, even if they have minor roles. As a result, we feel as if we know these people. McCauley's strengths and efficiency are obvious and we learn the roles and abilities of the other crew members. Mann doesn't stop there. We see one crew member, Chris Shiherlis (Kilmer), interacting with his wife (Ashley Judd). Chris has a gambling problem and it's affecting his marriage. His wife questions whether they should even be together. This type of depth is present throughout the movie.
Because we know the characters, it matters when something happens to them. Hanna's life is his job and he's essentially a hunter. McCauley is his current prey and we see Hanna using every available tool to find out what McCauley's crew is planning. As he learns more about McCauley, Hanna finds that he respects the man. They are similar in many ways and both are intelligent.
The most notable scene in the movie happens after Hanna pulls over McCauley in his car. He's not there to arrest him, but simply asks if they can have coffee together. The scene shows the personalities of both men and it's brilliantly written. Hanna mentions that it's his job to stop McCauley and that it's nothing personal. McCauley replies with a warning that he would have to take Hanna out if he got in his way. These are not threats, but calmly-stated facts. The scene is based on a real exchange between McCauley and Chicago cop, Chuck Adamson. If you think the scene is unrealistic, it really happened.
Heat is a drama more than anything else, but the brief action scenes are intense. The actors received training to make their shootouts appear authentic. Mann's focus on such details makes the whole story feel real. When we see people working at a crime scene, many are real forensic experts.
I can't promise 170 minutes of thrills, but the final scenes are among the most intense I've seen portrayed within the genre. All of the acting is good, but Pacino and De Niro understandably dominate things. If you enjoy character-driven stories, Heat is well worth your time.