I can only classify this film as a missed opportunity. While it did have a good storyline, worthy of a film noir, and some very good performances, especially by William H. Macy (you can almost see him crumbling under the weight of not just his crimes, but his cover-ups as well), it is tainted by the Coen brothers' directorial style. What made it intolerable for me was the amount of "quirkiness" that was injected into every single character, scene, and situation. Taken alone, each little quirk is not a big deal, but after so many of them, one after another, it just gets too much to stomach.
Some examples...
The title: The movie takes place mostly in Minneapolis (which isn't quirky enough -- that's where the Mary Tyler Moore Show took place, after all), and Brainerd (and nobody would go see a movie called "Brainerd"). About 5 minutes of screen time were set in Fargo, and Fargo has a quirky-enough sound.
"True" story: Just because a story is true, does that make it a better story? There is both good and bad fiction and non-fiction. So, what is gained by lying about whether a story is true or not? Quirkiness! See, if you believe this story is true, then all this quirkiness must be true too!
Names: Character names were given as Grimsrud, Lundegaard, Showalter and Gunderson. Apparently, Scandinavian-sounding names (especially with a double-a) are much quirkier than Pryce, Lopez, Rossi and Sheppard.
The weather: The snow and the cold serve no purpose but to make the characters put on parkas and snow boots, which make them look quirky. For instance, when the policeman was talking with the man shoveling his driveway, and had to put his hood up so far you couldn't see his face. Quirky! However, anyone who lives in a cold climate knows that when the sky is that grey and the snow is as wet as the stuff he was shoveling, it isn't all that cold...
Accents: Whether or not people actually talk "like that", what's the point of everyone talking like some country bumpkin, even the ones in the fairly large city of Minneapolis? Accents: quirky. No accents: not quirky.
Pregnancy: Apart from making the lead character wobble when she walked, and to give her a convenient excuse to throw up every once in a while, what exactly was the point of making the police chief pregnant? Ah yes, another quirk.
The old friend: A cop meeting an old high school flame at a bar. Sounds kinda dull, right? Well, let's quirk it up a bit. Make the cop a woman -- no, wait: a pregnant woman. Make the guy Oriental. Make it totally unnecessary to the plot. Now we're talkin' quirky!
By the time we get to the end, we're almost surprised that Macy's character sold plain old GM cars instead of Austin Minis or VW Beetles. The whole thing feels like the directors had no confidence in the subject matter, so they slathered on layer after layer of quirks in the hope the audience wouldn't notice.
In the end, it just becomes an exercise in frustration, as a movie that had everything going for it just turns you off after one wink and a poke in the ribs too many.