It’s in the top 5 highest grossing pictures 2 weeks in a row it opened #1 in it’s first week despite opening on fewer screens than other competing films. Most critics seemed to hate this movie but this is what I thought.
Playwrite/director/actor Tyler Perry lived on the streets for one year while he spent all his money financing his first play now he owns a multi-million dollar mansion in Atlanta and his own production company.
The screen-play “Diary of a Mad Black Woman” is based on his hit stage-play. In the movie just like the play his popular, reoccurring character Madea provides much of the comic relief in between heavy emotional scenes.
I saw the movie twice to support Tyler Perry and it is a good movie with a great balance between Humor and Drama.
As to why so many critics hated this movie…you either get “it” or you don’t but I definitely got “it” and would gladly see this movie a 3rd time while it is still in theatres. 
Extremely Brief Synopsis
Kimberly Elise (John Q) plays Helen a woman who is humiliated when she is literally thrown out of her house by her husband played by Steve Harris (Law and Order) she meets Shemar Moore (Young and the Restless) and a new relationship begins. In between the heavier scenes Tyler Perry uses several of his popular characters including Madea for comic relief so the movie never feels melodramatic.