Shaun of the Dead (which, come to think of it, I may have forced my family to watch on New Year's Eve many years ago).
This may be my favorite of the Cornetto Trilogy. At any rate, this and Shaun are neck and neck. And the reason, I think, I'm so impressed is that The World's End is willing to have a strong current of sadness. Not a heart-tugging moment, but a sadness that starts from the very first scene and continues throughout.
The sadness resides particularly in the manic and deeply addicted Gary King who "gets the band back together," cajoling his high school mates into completing the 12-pub pub crawl they abandoned back in the '90's. There's a desperation in his need to drink these pints dry, a kind of magical thinking as he makes his way from pub to pub despite the obstacles in his path.
If you don't know what the obstacles are, I'm not going to spoil it for you here. I will say, however, that Pierce Brosnan uses all his suavity to creepy effect in a brief scene. He makes his proposition sound so reasonable.
I may be influenced by the fact that I listened to interviews both with Simon Pegg and with Edgar Wright before seeing the film, which added extra insight in to some of what I saw. Great interviews -- though maybe only for fans.
I will also add that I vote for "blue bloods" over "blanks." Funniest scene in the movie. You'll see what I mean.