If you've ever enjoyed any Cohen bros movie (Raising Arizona, Fargo, Barton Fink, No Country for Old Men, O Brother Where Art Thou, etc etc) then yes, it's absolutely worth watching. If you've never seen a Cohen bros movie, Big Lebowski is as good a place to start as any.
I have a friend that used to throw annual Big Lebowski parties, where everybody is supposed to show up in a bathrobe and he would serve White Russians and In-n-Out while we all watched the movie. The movie is based on a real guy, although I think it's a fictional plot to play around with that kooky character.
I've seen Children of Men, and it was pretty good. Not Cohen bros good, but good enough that I remember seeing it (which says a lot actually)