My initial impression is that it didn't really have the same *immediate* impact on me as No Country For Old Men, which I think is an unqualified masterpiece. I think that's because NCFOM was more aggressive though. (Notice I said "immediate" impact - I saw this a couple days ago and haven't stopped thinking about it yet. It's layered and there's a lot you can chew on.)

Oscar Isaac is absolutely as good here as just about any other performer this year. He's the heart and soul of the movie, and he has something you can't fake: the charisma to make you care about him even though he's not a particularly nice person. (He also sings and plays all of his songs live, and does so quite impressively.)

His performance is really crucial because this is basically a pure character study. There's really not much in the way of traditional plot, which is fine with me but might somewhat hurt its reception with the general public. (When it ended, for example, the old guy next to me threw up his hands and went, "That's it?!?! It didn't *go* anywhere!")

Bottom line, it's exceptionally well-written, acted, directed, and shot. The performances and the music are really great. I'm not sure it's an instant classic, but I think history will regard it right up there with the best of what the Coens have to offer.

Oh, and to answer Colonelk's question above (VERY MILD SPOILER): Yes, Dylan exists in the universe of this movie, and at time the movie is set, Llewyn is more of a precursor/peer than a less successful version.