I really liked O Brother, Where Art Thou? and most of my friends that had seen it shared the opinion. It was an enjoyable movie and the songs and action were fun and the characters were likable.
When watching O Brother, Where Art Thou?, I saw it as more enjoyable when I viewed it as a stand-alone film as opposed to an adaptation of The Odyssey. The appeal of hero stories to me is definitely the characters and I think that the characters in O Brother, Where Art Thou? are more likable when they aren’t compared to the Odyssean characters. I want to watch the movie because I care about the story because of Everett or Tommy or whoever, not because I'm interested in the retelling of a heroic narrative that I've heard so many times before. The Odyssey wasn’t particularly likable in my opinion
because neither Odysseus nor Telemachus were especially likable characters. So when I think of Everett as a version of Odysseus, I care less about his story.
However, I think that if you don't watch the movie as an adaptation of The Odyssey, the plot takes a hit. The movie seems to just be a jumble of events that don't seem to really have any strong connection. However, when you look at them in the context of The Odyssey, you begin to see the parallels and the story seems to come together a bit more. When watching the movie, the sirens, the lotus eaters, the cyclops, etc, all seem so random until you see them as their Odyssean counterparts.
So if possible, I believe that this movie is best seen as a combination of a stand-alone film and as a film adaptation. However, I think this is hard to do. I think either way you watch it, either the plot or the characters take a hit.