Throughout his career, Lumet made some of the most intense character pieces of all time. He also helped direct some of the greatest actors to their best performances. He began his career with a film you may have heard of: "12 Angry Men." Lumet turned a gripping play into a gripping film, and showed his earliest instances of being able to use small spaces to create the most gripping tension you'll ever feel.
One of Lumet's other great examples of spacial tension was 1975's "Dog Day Afternoon." Perhaps the standard for all films about heists gone wrong, "Dog Day Afternoon" is still one of the great character-driven thrillers to come out of the 1970s. Without "Dog Day Afternoon," I wouldn't have an excuse to shout "Attica! Attica!" to random strangers on the street (not that I ever do that...). "Dog Day Afternoon" also marked one of his great films he made with Al Pacino, the other being 1973's "Serpico."
Perhaps Lumet's greatest achievement was "Network." "Network" is a little bit funny, and a little bit frightening. Some might wonder how Lumet and screenwriter Paddy Chayefsky were able to predict the modern nightmare of cable news in 1976. I guess you could attribute it to a little bit of undefinable cinematic magic. "Network" remains to this day one of the smartest satires I've ever seen. The line "I'm mad as hell and I'm not going to take it anymore!" is still the perfect anthem for those dissatisfied with the powers that be.
Even though Lumet certainly made some duds throughout his career, his greatest hits certainly make up for them. Not to mention, he was one of the most fruitful directors working, making films until he was in his 80s. Few directors could get such good performances out of so many actors and just direct to absolute perfection.
To those who aren't passionate fans of film, his name will not immediately ring a bell, but once you watch one of his films, you will never forget him.