Definitely top-tier Coens.
I wrote about my misgivings re: the ending on the General Movie Thread, but I don't think I made any sense cause I was trying not to spoil anything and I was (and am) still confused about it.
My problem is that (spoiler) up until the last two or three minutes, the overarching idea seems to be something like 'there is no discernible point to any of the terrible things God chooses to subject us to, and whether you commit good or evil acts it's not going to influence your fate, so just ride it out and try to remain a Serious person.' Seems a bit bland as a moral but they make something absolutely amazing out of it.
Then in the last sequence they appear to say, 'but if you make one small misstep like changing a student's grade in exchange for money, God might immediately kill you and the people you love most. So be extra careful, dummy.'
This really bothered me coming out of the movie as it seemed to contradict the previous hour and a half, but a few weeks later I think the contradiction actually makes the movie more ambiguous and rewarding. The Coen's are playing God, leading us along a safe path that seems to make sense for a while and then tripping us up at the last second.
Sorry to get so analytical about it, but I think the movie begs for this kind of discussion.