* It can and has been claimed by that the humor in XKCD is superficial, driven more by the dog-whistle power of recogition of cultural signs and signifiers than by a "true" or "significant" humor. Of course, an equally valid critical response questions the notion of "truth" and observes that the free play of signs and signifiers unmoored from a confining narrative core is a potent artistic force driving the work.
* A persistent debate between critical factions regarding XKCD is the question of whether those who claim XKCD is superficial don't understand the scientific and cultural references in the work, which debate is addressed by a direct recitation of those references in XKCD Explained.
* A common critical observation about XKCD that may not be obvious to the lay reader who does not closely track the comic is that it might be repetitive, which is to say that when the comics are stripped to their narrative kernel, many of the comics are essentially the same.
* Another common observation that may not be obvious to the lay reader is that it might be derivative, with comics repurposing the narrative and conceptual core of other, non-XKCD webcomics. This of course is an invalid critique, as XKCD exists intertextually with all other webcomics and is in fact enjoined to make use of and amplify the key ideas of those other comics.
* A more easily observable concern with XKCD is the relationship between the comic and gender, and in particular with sex, that concern being itself the observation of a subtext that implies that all references to sex are titillating to its audience, within which audience broad cultural norms have precluded actual experience with the reproductive act, and often contact with the opposite sex.
* Which of course drives us to the key concern with XKCD AND XKCD Sucks, which is that the authors of both works, being themselves bound to the norms of the media of English text, believe men are superior to women. Note the phallic symbolism of the letters "X" and "K", and the subordinate positions of the vaginal characters "C" and "D", the last of which represents (semiotically) the supressed but controlling desire of the male writer to maintain a pregnant state in the female reader.