This is the most recent Coen Brothers film. I found it a bit disappointing. Oh sure, there are a lot of funny gags in it (mainly involving Brad Pitt, a comedy genius), but it doesn't really go anywhere, and is a pale imitation of any of the Coens' previous funny films. It hurts that the film is largely devoid of likeable characters. Still, many of the jokes are funny. Never underestimate the comedy power of self-important stupid people. Appearances can be deceptive.
So is it all over for the Coen Brothers? I think this disappointment is their first original film (i.e. neither an adaptation, remake, or from some someone else's script) since the far superior Man Who Wasn't There. They are very different films, but in comparing them you can see how the mighty have fallen.