The misfortune of Marc Forster’s “Monster’s Ball” is that it invites too many invidious comparisons. As a portrayal of the realities of death row in an American prison, it doesn’t quite equal “Dead Man Walking.” As an examination of the way poisonous beliefs infect the succeeding generations in a family, it’s a runner-up to “Affliction.” As a depiction of the grief that comes from the loss of a child, it doesn’t match “The Sweet Hereafter” or “In the Bedroom.” Even in terms of restrained, minimalist performances from Billy Bob Thornton, it follows all too closely upon the ever-so-slightly superior “Man Who Wasn’t There.”

Still, if you can set aside all that, Forster’s film is actually very good. The central character is Hank Grotowski (Thornton), the head guard in the maximum security area of a Georgia prison where his son Sonny (Heath Ledger) works under him. The brooding, ominously quiet Hank is an unreconstructed racist–a trait that he’s inherited from his odious father Buck (Peter Boyle), a bedridden misanthrope who had also been a prison employee. Sonny, on the other hand, is a more sensitive, tolerant sort, though without much strength of conviction, and when his emotions overcome him during the execution of Lawrence Musgrove (Sean Combs), Hank is disgusted with the boy–an emotional reaction that leads to family tragedy. Shortly afterward, Hank encounters Musgrove’s widow Leticia (Halle Berry), who’s taken a job as a waitress in a diner he obsessively visits, always for a bowl of chocolate ice-cream, which he eats only with a plastic spoon in a habitual booth. On one stormy night he’s compelled to help her after an accident befalls her son Tyrell (Coronji Calhoun), and they gradually enter a halting friendship which necessarily challenges his inbred ethnic hatred (and brings out the worst in his father). The ultimate question is whether these two damaged people can overcome their individual losses and come together despite the obstacles which separate them–or, to put it in the way that scripters Milo Addica and Will Rokos frame it a mite too ponderously, whether Hank will be able to find happiness (which is what “leticia” means in Latin, of course). Even more broadly, the issue is: can the present escape the past, or must we remain what our families have made us?

The coincidences that propel the plot of “Monster’s Ball” (the title refers to an execution without lawyer, minister or family present) are severe, of course, and Forster’s very deliberate staging accentuates the essential implausibility of it all. Still, the overall impact is considerable; this is an affecting, thought-provoking film despite the plot contrivances on which it depends. Thornton gives his third superb performance of the year (along with “Bandits” and the aforementioned “Man”), and Berry is excellent as well: the hesitant nature of their courtship is beautifully caught through the use of silences rather than reams of dialogue. Both are especially effective in their relationships with their children: Hank’s final confrontation with Sonny is extraordinarily powerful, and a scene in which Leticia berates Tyrell for his overeating is painfully vivid. Ledger and Calhoun are very fine as the youngsters, too–the Australian heartthrob is particularly to be commended for taking such a risky part–and Boyle is spectacularly loathsome as Buck. Surprisingly enough, Combs is not lost in this company; he paints a nuanced, even touching portrait of the dignified, doomed Musgrove. All the performances are enhanced by the splendid wide-screen photography of Roberto Schaefer.

“Monster’s Ball” is a spare film, almost as laconic as Hank is himself, and some in the audience will find it ponderous, even emotionally desiccated. If you’re willing to surrender to its peculiar rhythm and allow it the necessary space to grow on you, however, you should find it a remarkably moving experience.