I'm pretty sure I wasn't savvy enough to see this when it first came out in theaters. I think I had seen Spaced at some point when I was in college (2001-2004) although I didn't see the full episode and my memory of what happened. For some reason I thought it was a sitcom based in an English town where there were different crazy background stories going on in the background that the main characters would come perilously close to without running in to or learning of the craziness around them. I thought I saw an episode where there was a spy story going on that Simon Pegg's character had no idea was going on. As it turns out, none of that ever happens in the show Spaced and I have no idea where I got that impression, but it is similar to the early scenes of Shaun of the Dead where he has no idea he is surrounded by Zombies.
This is such a dense movie with references, parallels in the story lines, and jokes throughout. It's a comedy that almost ends with a murder suicide. Frank Darabont would learn a couple of years later with The Mist that viewers don't care for that when you follow through with such a threat to the audience. In Shaun of the Dead, Edgar Wright takes us there, he kills off beloved characters and brings the movie to a dark an violent conclusion before screeching the brakes to show the world going back to normal, with a twist. It's a bit of a perfect analogue to the life back to normal after a shared tragedy that was seen after 9/11. The world was shaken only to have us feel like it is normal to take our shoes off in the airport security line.
This was the first broadly released film by Edgar Wright and he came out swinging with one of the best comedies and one of the best horror/sci-fi films ever. Luckily, he has had the great sense to keep making movies with the Simon Pegg/ Nick Frost team, and his film (Scott Pilgrim) aside from them have been just as amazing.