Reduced to their basic elements, these two comedies are very similar. Both involve a bunch of friends getting together for a very wild night, but in both cases something very peculiar and unexpected happens part way through. One film has an invasion by aliens from outer space, and the other has the Apocalypse, complete with rapture, fire, brimstone and demons running amok. The comedy of both films comes from how the characters react to the situation that they are in, which is one of great danger and earth shattering consequences.
This Is The End spends a lot of time on trivial details, self reflection, arguments and crude humor. It is a somewhat entertaining movie but what I like better about The World's End is that it has much more plot. Both movies are smartly written, but I think The World's End does more with its story.