Not that The Big Lebowski was exactly a sober, disciplined affair. But O Brother sorta makes it look like one. For one thing, Brother is basically a musical, which in this day and age would be hallucinatory enough even the visuals accompanying the songs weren't things like the KKK doing Busby Berkeley or John Turturro in a ludicrous fake beard doing a spastic macarena. The songs themselves also seem to be chosen in large part for their cheese factor (though the "hit single" is so catchy that it's easy to believe it could spark the craze the story calls for, and the sirens' song is indeed hyp-mo-tizing.) And then you have the Limboland settings, the beyond-cartoonish, mannered performances... it all ends up feeling a bit empty. Still worth checking out, though.
Quick story: I didn't know when and where this movie was playing, so I swung by moviefone.com and entered "o brother where art thou" in their little search window. The site replied, "Match found! Did you mean: 'Dude, Where's My Car?'" Which pretty much sums up the divide between what intelligent filmgoers want and what the entertainment industry provides, dunnit?