It's a mini-boomlet in humanity-faces-Armageddon movies. But this is much, much more fun to watch than Melancholia, even though it lacks Kirsten Dunst's bazooms.
The culprit in this movie is "Matilda", an asteroid that's on track for an inevitable collision with Earth. We're informed right at the start that the usual Bruce Willis/Robert Duvall mission to save the planet has failed, so what's left is to follow the odyssey of Dodge (Steve Carell) as he tries to deal with his wife (literally) running out on him. (Nice touch: Dodge's wife is played by Steve Carell's actual spouse, Nancy.)
The large-scale reactions to doomsday are as expected. Some engage in violent anarchy; some seek out hedonistic excess in various combinations of sex, booze, and drugs; some plan for survival; some wallow in the mellow fellowship of family and friends. But Dodge becomes obsessed with reuniting with his high-school sweetheart, Olivia. He pairs up with Penny (Keira Knightley), a ditzy weed-loving free spirit. They set out in search of Olivia, but encounter a number of colorful characters on the way.
It's unpretentious and (although not billed as a comedy) very funny in spots. And mawkishly sentimental in other spots. But overall, very watchable. It probably helps that Steve Carell is an expert in portraying sympathetic characters; in less capable hands, Dodge would come across as a whiny, effete loser.