Spaced was about a bunch of SF fans, not unlike me and my mates, and it achieved a brisk economy by using masses of pop-cultural references, which allowed the plot to bound along without too much exposition between jokes. I was on a mailing list which Pegg posted to sometimes and he understands what he is doing, and does it well IMHO.
Remarkably, he manages to transplant this method quite succesfully into film. He uses the audience's familiarity with Zombie movies to allow the zombie plague to build up in the background of shots, and through suggestion, without the lead characters realising what is happening. I personally found that funny and chilling. I think the first half of the film, which uses this method, was the best bit. For example, he's talking to a friend about his love life, and in the background, you see a woman collapse at a bus stop. Because we understand the genre, we extrapolate readily from such hints.
The other subtext he can convey, by using such a method, is to draw out attention to how zombie-like people are when they are going about their daily routines. Not an original point, but well made.
My alter ego Dylan Moran (see pic) was in it, as a twat called Dave: 'I'm not a chartered accountant, I'm a lecturer'. He continues to be me. Want to give away spoilers at this point but I won't.
The second half, as they battle the zombies, wasn't bad, but I thought it could have been faster and more pounding. They do homage Tarantino (of course) but I would have sloshed it on a bit heavier. They are in a pub with a juke-box for heavens sake, so I would have had a constant stream of British rock classics playing in the background as the heroes 'go out there are twat 'em' (to quote Dave Lister).