Despite using the same (approximate) language, there are marked differences. British humor employs more irony and absurdity. American humor uses more slapstick and visual jokes. It tends to be more obvious. That doesn't mean that there isn't some overlap. "Monty Python" was very successful in the U.S. , partly because it was clever and funny, but also because of its novelty. Americans at the time hadn't seen anything quite like it. Compare "Monty Python" with some of the more famous "I Love Lucy" or "Carol Burnette Show" episodes and I think you'll see the difference. That doesn't say that one brand of humor is superior. Humor is often the hardest thing to translate from one language to another and one culture to another - even if the cultures speak the same language.

I think FDMaxey has explained it very well. :) One other note is that I find American humour is often "signposted". That is, it is obvious when something is a joke and when something is not. British humour, by comparison, demands much more attention. I recently "tortured" a friend with The Office (British version - the Christmas special) and most of it was mysterious, even boring, to her. I was guffawing non stop.