As a TV mogul lays dying, the lives around him unravel, as the past catches up with them - the wife who married for money, the son who disowned him, and others caught up by the game show he created. Eventually the numerous strands of the story are reeled in and resolved, through a balance of redemption against retribution of which Nick Cave would be proud. Much has been made of the film's length.
Magnolia requires patience - it is long.
Take a cushion, and take the risk. One more thing. Tom Cruise is in this picture. Do not be afraid. And his catchline is hilarious, but far too rude to write on a respectable site like this.