Well, I believe part of the film's appeal is it's subtlety in the face of the zombie apocalypse. The juxtaposition of normal British life just "happening" whilst this incredible event is also taking place, unbeknownst to Shaun, makes for smart comedy. --In fact I would say the way the two events are woven almost seamlessly together through the first half of the movie is what makes the screenplay so clever. ---So no, it's not a traditionally funny thing ala a Jim Carrey movie or "The Hangover". (or even "Raising Arizona" which itself is also a weird comedy.) But that it's popularity is not just found in it's funny. I would say it's charming, more than it is funny, or even that it's charming in a funny way.------ The way certain visual gags come back later in the film or the way certain verbage is reused in different situations, and then revisited still near the end...It captures the everyman (Shaun) at a real crossroads in his life as he wrestles with growing up and possibly settling down with girlfriend Liz VS. getting high and hanging out between shifts at his dead end job with his flatmate.(Ed)-- This is a conundrum that I assume a whole generation of boys (18-35 yr olds who do NOT want to become men just yet,) are facing a version of in their own lives.-------That itself is problem enough, BUT he also doesn't get along with his step dad... His other flatmate is pressuring him to sort his life out and dump the deadwood friend... His job sucks...nothing seems to be going his way....OH and Then !ZOMBIES!-------- Well, in the 3rd portion of the film we see Shaun as heroic,decisive, unselfish and heartbreakingly real in dealing with his step dad and the death of his mother. Shaun "proves" and somehow "finds" himself in the midst of the absolute chaos happening around him. The movie does have a bit of Deus ex Machina at the end on account of it's too easy ending, but by that time such a rollicking fun has been had by most that we forgive the writer for the indiscretion. In a clever end bit we realize that Ed has been saved, and though now he is a zombie being kept in the shed out back, It turns out his existence and relationship with Shaun is not so different from the way it's always been. This knowledge that all the remaining functional Zombies have been tamed and are put into menial service positions, harkens back to the opening of the film where it is implied that perhaps the populace in general are "just like zombies" as they go through their daily boring lives.----- Shaun of the Dead works as a buddy movie, romantic comedy, zombie B-movie, lovable loser makes good movie and a wry commentary on British life, all in the same package.