I actually saw it very recently... and I'm not sure I can. I loved it, but I didn't fully understand it, and I really want to rewatch it (which is rare for me). John Goodman is amazing in it, that I'm certain of.
I mean clearly it's a morality tale and Barton Fink is experiencing some version of Hell, but I'm not sure where the lines are drawn between reality and hallucination/allegory. I'm sure the New York scenes are real, after that... I need to rewatch it. I want to say the scene where he completely and blatantly ignores anything Charlie has to say (their first scene actually) should be real, because it feels like that pretentious self-involvment is what he pays for in the rest of the movie, but I'mnot sure where the wallpaper thing starts to come in, as that's the first clear sign that the film is going in a surrealist direction.
And sure, The Dude is a nice character to be around, but he wasn't that fascinating to me.