Has great elements but isn't a great movie
There are some moments that feel really great, anything involving the chase of Anton vs. Llewyn. Some shots are beautiful. Otherwise, the story is standard, wrapped up with old people talking about how the world has (not) changed to add a thin layer of commentary. The cast is standard. The beginning is slow (it needed something to keep me interested and the ending (while i agree straightforward endings are dull).
I gave it a 7/10 for Bardem, but it would probably be a 5 or 6 with any other actor.