From Lingan's review:
It’s not the happy ending of Slumdog Millionaire that bothers me; happy endings can be one of the great rewards of good art, movies or otherwise. Rather, it’s the cheapness of the ending—its reliance on the shocking and brutal events leading up to it—that makes the movie’s emotional payoff feel undeserved. Boyle and his screenwriter Simon Beaufoy seem uncertain of their ability to actually engage an audience’s emotions, so they bombard us with nightmarish images and sell them as tragedy. Then they finally reunite their protagonists at the film’s end and sell it as happiness. But every emotion in Slumdog Millionaire is broadcast at 10,000 decibels; the movie is a screaming neon cartoon of human experience, not an effective framing of hopelessness and redemption like the best inspirational movies—One Flew Over the Cuckoo’s Nest, The Landlord, The Grand Illusion, The Elephant Man, Sullivan’s Travels, Nights of Cabiria, or even It’s a Wonderful Life come to mind.
From the LAT:
Those who claim that "Slumdog" is filled with exaggerations and cliches need to remember that this is fiction. In documentaries, exact representation, uncolored by personal beliefs, might be the goal; in feature films (and fiction and painting), it isn't necessarily so. When one accuses "Slumdog" of exaggerations and caricatures, it is similar to accusing Van Gogh of distorting his sunflowers or M.F. Husain, one of India's foremost living artists, of not getting his horses' colors right. In "Slumdog," Boyle is following the convention of the picaresque, a genre that depicts with energetic abandon the many misadventures of a hero, usually of low social class, who ultimately triumphs over a corrupt society by using his wits.