Stephanie Zacharek writes a spot-on review for Salon.com:
Hopefully I'll be writing more about "Knocked Up" in the future; about the bright future of R-Rated comedies, about the contradiction of a sweet film that contains a lot of harsh language, about the surprising morality in what appears to be a stoner movie, comparisons between Judd Apatow and Kevin Smith.... ooh, this is fertile ground.
...Apatow uses an unplanned pregnancy -- a jarring event that's also, perhaps paradoxically, one of the most natural things in the world -- as a device to explore parenthood and the nature of long-term partnership. "Knocked Up" isn't at all precious about either: At first, Alison isn't even so sure she likes Ben. And when she invites him to dinner to break the news (they haven't seen each other since the awful morning after that fateful night), he reacts just like the immature stoner bonehead she believes he is. "I assumed you were wearing a patch -- or a dental dam," he sputters, cruelly suggesting that after all, it's the woman's responsibility to take care of such things. He doesn't even have to know the right words for them.
But Ben is at heart a sweet guy, and he and Alison tentatively move toward common ground, making the kind of connection that could turn into love. They also fight, in ways that bring out the worst in each of them: Alison is impatient, demanding and judgmental; Ben is a little boy who's reluctant to grow up. The male-female arguments in "Knocked Up" are sometimes so vicious, so indicative of suppressed toxicity, that they're painful to watch. At one point Debbie advises Alison on how to gain the upper hand with a partner: "You criticize them a lot until they get so down on themselves they're forced to change." Her pert, cheerful certainty on this matter is what makes the line so funny, and also so horrifying. Pete has his own way of dealing with marital pressures. He's keeping a relatively benign secret from Debbie, and when she discovers it, she lashes out at him -- and the ensuing confrontation makes you feel horrible for both of them. Apatow has no compunction about going for uncomfortable laughs, as well as breezy ones.
This is a romantic comedy that's unafraid to face human suffering dead on. And yet, in the end, it's all the more joyous for that. "Knocked Up" is a beautifully shaped piece of work: There are no slack patches, no gratuitous feel-good moments -- if you walk out of "Knocked Up" feeling good, that means you've earned it.