Intelligent, Witty, and Disappointingly Crude.
So, XKCD has a reputation for being one of the best webcomics out there. I disagree. Sure, it has some amazingly obscure jokes that require mathematical knowledge to understand, and sure it is often funny, but, more often, it descends into mean-spirited humor.
For example, Black Hat Guy, upon hearing the old riddle involving the three words in The English Language that ends in "ngry", cuts off the jokester's hand, saying "Communicating poorly and then acting smug when you are misunderstood is not clever. I hope we've learned something today". Apparently, making inane riddles is a crime worthy of dishandbobulation.
But really, most of XKCD is based around communicating poorly and then acting smug when you are misunderstood. That's the basis of all the really obscure mathematical jokes.
Speaking of acting smug, that adjective could describe most of the comic. It's very highbrow, and it's often condescending towards Liberal Arts Majors, Pedants, people who hate Neologisms, internet nerds, string theorists, and people who have eclectic interests. Many strips are written purely to be annoying to the reader.
Yes, it is funny, but it's not the type of humor I like. One out of five stars.