Not my favorite P.T.Anderson movie, since as I pointed out elsewhere, I see the father-son obsession in American films an intolerable cliche. But the acting is very strong, and the plot, in spite of all the drama, is quite plausible.
Philip Baker Hall here plays an aged and tired professional gambler, who takes a lost soul under his old, tattered wings, first driven by guilt, then by genuine affection. The lost soul, convincingly played by John C. Reilly (the cop in "Magnolia"), turns out to be a wretched loser, prone to self-destruction. The tension of the film is built on Hall discovering one problem after another, stoically accepting the cards Fate deals him, and move on with a resolution.
The movie often feels like taking sips out of a cup of bitter and acidic coffee, with one cigarette after another, in a roadside diner. Hey, who's complaining?