This is a very bleak, obscure comedy by the Coen Brothers, most notable for making movies like "Fargo" "The Big Lebowski" and "Burn After Reading." People need to know that compared to those films, the humour in this movie is not obvious and very very dry and obscure. It's deep and complex, with lots of themes including Judaism, anti-Semitics, drug use, divorce, death, terminal illness, child pornography etc.
The film is set in the 1960s and it is based around the life of a highschool teacher who is cursed with bad luck. Everything is bad in his life, and some people might find this boring, but if you look deeper into the whole thing, there is lots of very funny humour.
With his wife wanting a divorce, his son's bar mitzvah coming up and a korean student conning him into giving him a good exam mark, he is very stressed and consults three different rabbis, trying to find out the meaning of his life.
Some of it can be boring and bleak, but I found most of it was very subtle and very funny. The ending may be frustrating to some, but I really enjoyed this film and thought it was classic Coen Brother's style. You actually feel very sorry for the main character and what he's going through.
There is some swearing including f***, among others, some sexual references including a fantasy sex scene where a woman is thrusting on top of him (brief and nothing shown), a man is accused of sodomy and child abuse, people are shown smoking marijuana and getting high (comedic), and there is some violence including a man being shot in the neck (from a distance.)
All in all, I really enjoyed A Serious Man, but I think you have to have an acquired taste to really embrace the feel and mood of the comedy, and the subtlety of it. :)