I'm going to help you enjoy this apocalyptic comedy a little more than I did. There's a blink-and-you'll-miss-it scene near the beginning that shows Simon Pegg in group therapy and remembering this scene is critical to enjoying the next joyless forty minutes as Pegg plays one of the most abrasive characters in recent film history. Pegg's Gary King is struggling with mental problems and it goes some way to explaining his rotten behaviour. This info will help - honestly!
Gary King's life peaked one day in 1990 when he and his five chums finished school and went on a major pub crawl, but Gary and co. passed out long before hitting the titular twelfth pub and it's niggled away at him ever since. So he decides to get the gang - Frost, Considine, Freeman and Eddie Marsan - back together to finish the job but if he was planning on reliving the old days it's not going to happen: the gang aren't the same guys they were... and no one else is either - has the entire population of their home town been swapped for aliens? Better keep the head down and get another round in.
It's around this moment, just as you're in danger of hating Pegg, the movie, life, the universe and everything, that The World's End gets down to business - the gags become less caustic and the action is let loose. With such a lengthy setup, it's almost a surprise when Pegg and an insolent teen go head-to-head in a pub bathroom in a fight a scene that turns into a funny free-for-all; the blood and guts of Shaun and Fuzz, however, are replaced by the aliens' blue goo, which doesn't have the same effect.
While The World's End suffers from the same problems as Hot Fuzz, relying on too many movie references - Body Snatchers, Village of the Damned - and being far too long for its own good, there's a decent brisk pace to the enterprise. And what it has to say about childhood friendships evolving into adult ones is sweet... well, it would be if one could decipher what they were saying in the bombastic and drawn out ending. But it's nice that there's an attempt at least.
Overlong but (eventually) funny - just remember that group therapy scene.