I haven't seen all of the movies from the Coens but I have seen quite a few. A Serious Man, The Big Lebowski, No Country For Old Men, Barton Fink, Fargo etc.
I've got to say. I've never watched a movie that involved one of them that wasn't at least mediocre. I LOVED A Serious Man and The Big Lebowski. Barton Fink didn't click as well with me although I enjoyed it.