Most of the reviewers of this film have hit the nail on the head. The script simply is not believable. Everything else is there: the usual impeccable performance by Jack Nicholson, the supporting cast up to par, and Penn grows as a director, perhaps not quite relaxed or self-confident enough to let things flow once in a while, instead of holding such tight reins over each moment of the film. One assumes he will eventually become one of our country's great directors.
OK. As the film moves forward, it becomes more and more unbelievable. And at its end, the viewer cannot be sure whether the main character has gone insane or is simply very, very drunk. This great drunkenness, by the way, has never before been revealed in the film. Nicholson's character has been sober throughout. We are informed of this problem by another character near the film's ending.
While truth stretches truth, one only hopes that these wonderful performers will better themselves with more honest, quality scripts in future. The movie is worth it for the performances, I suppose. But five thumbs down on the story!