An oft-repeated platitude tells us that the whole is greater than the sum of its parts. But there are times when, conversely, distinct halves do not add up even to that whole. Such is the case with début feature director Darren R. Grant’s Tyler Perry all-star showcase, Diary of a Mad Black Woman, where two potentially related parts, and more, are effective after their manner but so disparate in tone that the thing falls apart.

Screening audience reaction bolstered the suspicion that Perry’s adaptation from his own stageplay will delight African-American women of a certain age, and that rarity may in itself provide box-office oomph. But in terms of unity as a movie, the mix of social commentary, racial-feminist empowerment wishfulness, Terry McMillan soap, slapstick, substance abuse, and sexual and flatulence jokes -- all topped with God, gospel and good ole downhome Church -- well, this film conglomeration is tough to take.

Not always bad but consistently obvious music throughout betrays Grant’s music-video background, as do opulently unimaginative camerawork and sets, where Atlanta mansions shame Kane’s Xanadu and even “ghetto” residences are beyond most folks’ wild dreams. Combined with unpardonable lapses of minimal taste, as in vengeful yuks as a paralytic comes within an ace of drowning in a marble bubbled bathtub, the terrific swings back and forth cheapen the very issues that are raised and, supposedly, resolved.

Enter mega-lawyer Charles McCarter (Steve Harris) and wife Helen (Kimberly Elise), dressed to the glittering nines for a society do honoring him as Citizen of the Year. Her voiced diary “I am so proud of him” fades to his acceptance speech nod that “I couldn’t have done any of this without my wonderful wife of eighteen years,” etc. Applause.

Fade to the couples’ ride home, a far different picture. After sweet Helen offers anniversary eve intimacy, surly Charles  responds with stony indifference, heading off for late-night “office work.” His many affairs have become one lover, with a child, and he orders the wife out of the house that is his by pre-nup, and out of his life. To ensure the split, a U-Haul appears and is loaded with what’s hers. Wounded and angry, she berates the driver and arrives alone back in the ghetto from which she and Charles once fled.

Not just anyplace, but the house where she started, and where the film starts to crack apart. The large, neat, lawned dwelling is the domain of grandma figure Madea -- “short for ‘mother dear,’ Perry explains,” but hinting mad-angry, as well, and Colchian Medea, legendary Jason’s wife extreme in love and revenge. Not Tyler Perry in drag, for the writer-actor is better than that, Madea (Perry) is a bustier oversized Dame Edna, pistol-packing, lustily trash-talking, pot-smoking, take-no-prisoners, feminism-spouting all-encompassing ego. She will not let Helen mope -- nor her own lame randy brother Uncle Joe (also Perry) have his way -- but sets the girl out to get her propers.

Also around are Cousin Brian (again, Perry), an honest lawyer raising two kids because Debrah (Tamara Taylor, too attractively unravaged for the rôle), his wife and Helen’s childhood buddy, is a hopeless junkie. Brian’s friend Orlando (Shemar Moore) shows up, a hard worker who happened to be driving the U-Haul as a favor. Surrounded by, lost amidst, outrageous comic activity, and some good throwaway lines -- “the City of Atlanta versus Bobby Brown” -- Helen will try to pick up the pieces of her life, while Orlando tries to pick up Helen.

Respectfully chaste, cornrowed soulful hunk Orlando is a Christian girl’s dream-in-a-million who even “smells so good!” If he is too good to be true, hubby Charles is not: a murderous coke-dealer (Gary Sturgis) surfaces from the model citizen’s shady past to extract payback, giving Helen, too, cold revenge that so ties her soul and body that, abandoning Orlando, she falls thrall to that sterile emotion. From Willow Tree Nursing Home where Charles has thrust her, Helen’s mother Myrtle (a Cicely Tyson shrunken into her first screen appearance in ten years) comes toting her Bible warning that vengeance is the Lord’s while man’s is to forgive. For too long a film stretch, Helen does not heed, but ultimately she will get the idea. In case we haven’t by now, gospel services will remind us, all wounds will be cauterized and healed, good rewarded, bad punished but repentant.

So many pieces cannot be forced into cohesion. Ironically symbolic are the end-credits, listed alongside a medley of cut bloopers and howlers, each separate and unrelated, if at times a few good seconds.

(Released by Lions Gate Films and rated "PG-13" for drug content, thematic elements, crude sexual references and some violence.)