Those words are exactly how I've described their movies. It seems to be impossible to pinpoint what is different about them. O Brother, Where Art Thou? is up there as one of my favorites as well.

I'm curious as to how you would enjoy Barton Fink. It is a little slower-paced and dark, but has that subtle Coen humor. Another one that fits well with the theme of this BB is Miller's Crossing. Both are very well done with that "something" that makes the Coen Brothers movies unique.

But I think Raising Arizona is another one that you might like since you seem to enjoy the more lighthearted movies they have done. It's about a couple, one is a con (Nicholas Cage) who, while arrested, meets a cop (Holly Hunter) and they fall in love. They are unable to conceive a child so they decide to steal a baby from a family who has quintuplets. As you can imagine, it's as strange and funny as anything the Coens have done

Please let me know if you watch any more of their movies as they are my favorite.