Spoiler Alert 98% of the above user comments have totally missed the idea of this movie, and yet some have gotten it exactly correct without even realizing it. Here is THE WHOLE POINT OF THIS MASTERPIECE MOVIE...
Those that stated that the first 2/3 of the movie is boring and then it starts to pick up when the action begins, have unwittingly seen the plot, and masterfully fulfilled its premise. See, Barton Fink is a boring, artsy, impassioned Jewish writer, that gets one lucky break, and is instantly summoned to write a movie that the execs are sure "will be a winner" (no pressure there, right Hollywood?). But since he is so much an "artist", he cannot lower himself to the level of writing a simple wrestling film, desiring instead to write witty stories about "the common man", films that "really mean something". Then he refuses to listen to common man stories, stuck instead on his own ideas of what that should be.
Well, OK, what is obvious here? Well the Coens for one, are Jewish WRITERS/ FILMMAKERS, who got one lucky break, "Blood Simple", and then were given the open door to make Hollywood films, are always branded as mere "artists", too idealistic for the majority of the masses (their movies are rarely fully appreciated or understood, and make only a small profit, but their genius high critic ratings keeps them afloat). So THEY ARE Barton Fink, quite literally and intentionally. It is THEIR personal tale, ensconced in a symbolic cloak.
Summary: Barton wants to write for the common man, and yet what the common man wants to see is this dumb "B"-rated wrestling flick, not some heartfelt idealistic piece about some friendly yokel. They want predictable mystery, unadulterated violence and blood, guns blazing, detectives crunching, and loud sex. As Barton stares at the image of his idealism (the beach picture), he longs for his ill conceived idealism to take form and materialize onto the paper. But of course it is a failure, because he sees himself as an "artist", not as a business man with epic visions.
Which is why finally, the mysterious Audrey (the real writer he is supposed to consult), who always helps Mayhew's stories out of a jam, becomes the catalyst for this story as well, by initiating the sex/horror/detective story as soon as she is asked to. Normal writers apparently are like either Fink or Mayhew, but she sees through to what makes for real-world successful writing (not some dorky contrived "common man" story), and she initiates the final action-filled finale immediately.
This is PURE GENIUS! "Adaptation" as one user here mentioned is like this film, because of the similarity in how the plot loops back in on itself. But this one is much more subtle, to the point where the "common man" would not even understand this movie, and thereby fulfill its message, that all people want are the action films that Hollywood dishes to us, just like the mogul states over and over, and we see delivered on the last third of the celluloid. In the end, Fink realizes his idealism, that what he really wanted is to get his artistic view rejected, so that he can maintain his idealistic (unrealistic) outlook, which is his true passion, the "fight" for self fulfillment. This is personified by the appearance of the girl on the beach, with Fink still not realizing what would be in the box, because he doesn't comprehend Hollywood thinking or action movies (or "mainstream" movies or plots). But he has achieved his goal, as has the movie for Joel and Ethan, as both being an incredibly well-thought and executed film, both an art flick, and an action piece with more perfectly executed symbolism than anyone since Wells.
Now you know why it won all the Cannes awards that year, and why these two brothers from St. Louis Park Minnesota are gods of the art film, while the contrasting Warchowski brothers were once gods of the "common man" film (the first Matrix at least). The Warchowski's even named the subtitle of the Matrix Reloaded as "The Burly Man", which if you look closely (zoom in), is the name of Barton Fink's mystery screenplay, thereby once again fulfilling the intention of this film to the fullest (that what common people want is delivered like clockwork in the Matrix), just like pure Bible prophecies.