Up until now, Paul Rudd has been content to sit in the back seat. Apart from a funny but nondescript star turn in Role Models, Rudd has mostly bided his time on the fringes of the various Team Apatow productions, churning out one memorable supporting performance after another, plus the occasional bit part in the likes of Night at the Museum. That he's developed a small but enthusiastic fanbase anyway speaks to his star potential.

I Love You, Man is a sweet, amusing, and perfectly acceptable comedy all around, but it's exciting because it marks the point where Rudd finally begins to stake out his territory as a comedian and a leading man. As Peter Klaven, the happy and level-headed real estate agent who discovers, upon proposing to his girlfriend of eight months, that his total lack of guy friends will result in an all-female wedding party if he doesn't act fast, Rudd combines a nice-guy earnestness with a simmering nervous energy – he's like a less sarcastic Albert Brooks or a more self-conscious Steve Martin.
What surprised me, given that the comedy of Rudd's career-defining roles to date has been either largely physical (the beaten-down husband in Knocked Up, Rachel Weisz's nerdy-turned-studly "project" in The Shape of Things) or intellectual (his "smartest guy in the room" shtick in Role Models), is how verbal his performance is here. The film's longest running gag is Peter's aimless, embarrassed stammering, his attempts at breezy nonchalance turning into awkward symphonies of nonsense syllables. Another – probably the funniest – involves the revelation that Paul's various impressions (another attempt at cool) all turn out Irish, which somehow leads to Rudd doing a hilariously attenuated James Bond routine. It's a showier comic performance than anything Rudd has done before, but he seems comfortable and at ease -- even when Peter is anything but.

Rudd's foil in I Love You, Man is Jason Segel, channeling Owen Wilson as Sydney, the laid-back, cheerful slacker whom Peter targets as his new best friend. It's a perfect complement to Rudd's constant, barely-contained panic; the film sort of works as a subtler, less hokey version of the classic mismatch buddy comedy. To his credit, Segel mostly just stays out of Rudd's way in a role where the temptation to try to steal scenes must have been difficult to resist.

The movie, written and directed by John Hamburg (Along Came Polly), is uncommonly intelligent and finely tuned. It's occasionally raunchy, but surprises us by veering in a serious direction: a running joke about blow jobs turns into an almost credible discussion of Paul and his fiancée's sex life. It has a way of setting up a joke and blindsiding us with the punchline thirty minutes later. There's one rewarding scene, involving a party toast, where the joke dawns on us halfway through in a simultaneously hilarious and horrifying wave of comprehension.

Hamburg has a sentimental streak, but it's not always overt, and he knows how to be sweet rather than cloying. At one point late in the film, I surprised myself by letting out an involuntary "aaw." And though I Love You, Man is occasionally a bit clunky – there's a big false crisis in the third act that lasts about thirty seconds, and there's ultimately just a bit too much pompous speechmaking for my tastes – it avoids most of the pitfalls I expected to see. There are no contrived dramatic revelations – something stupid like Segel's Sidney turning out to be desperately friendless himself, for example – and no big scene where Sydney gets angry at Peter for initiating a friendship under false pretenses. And the film features a true rarity: a gay character (Andy Samberg, playing Peter's brother) who is not a flaming, limp-wristed stereotype.

The film draws the obvious parallels between romantic love and deep platonic friendship, trying to squeeze a lot of laughs from Peter's nervous, deliberate "courtship" of Sydney. The joke withers and dies after a while, but it's not often you see a movie that focuses on friendship and leaves romance in the background. (Though Rashida Jones gives a lovely little performance as Peter's fiancée, with Hamburg shrewdly making her character kind and encouraging rather than a shrill nag.) That it handles the subject intelligently, without turning sappy and maudlin, is less common still.

But in the end, I think I Love You Man will be remembered as the movie that turned Paul Rudd from a dependable supporting player into a comic force to be reckoned with. He's a genuine talent: a funny, smart, relatable comic with the acting chops to back it up.