In interviews, Michael Cera has been ambivalent about his newfound fame. He's even expressed gentle skepticism regarding the Arrested Development movie everyone's buzzing about. I'm sure he has legitimate personal reasons to be concerned about his celebrity – it can't be easy for someone who doesn't have a huge personality, and who isn't a natural attention hog. But we fans and viewers also have reasons to worry. Foremost among them is the concern that Cera's popularity could drive him to roles where his talents are wasted. Indeed, as this fall's Nick & Norah's Inifinite Playlist demonstrated, it's already begun to happen. For the first time in the comic's career, his presence hurt the project instead of helping it.

In my first go-round with Nick & Norah, after reading the book and before seeing the film, I was optimistic that the role of Nick was just the opportunity for Cera to expand his range – play a character who is a little more confident, a little less tentative and hesitant. Sadly, that's not what happened. Instead, some subtle differences aside, Cera transplanted his (very funny) stock character from Arrested Development, Superbad and Juno into a story where that character wasn't needed, or welcome. In the process, he turned what could have been a sweet, moving romance into a tepid, if still amusing, teen comedy.

Nick & Norah's Infinite Playlist is ostensibly a story about two interesting, self-possessed "indie kids" who have a whirlwind one-night courtship while searching for a "secret show" that their favorite band is slated to play somewhere in New York City. The novel was written from the perspectives of both characters, alternating chapters. As they take stock of their dreams, their hang-ups, and their past relationships, they come to realize that they're meant for each other. They have individual trajectories but they meet in the middle.

But the way Cera plays Nick doesn't put him and Kat Dennings' Norah on equal footing. Cera's comedy is almost entirely reactive. His characters do very little on their own; when they do, it's played for laughs (e.g. Superbad's Evan suddenly deciding to grab his detergent can full of alcohol and hoof it from the police). Emotionally, his characters' breakthroughs and big moments take the form of their sweet, often bewildered responses to others. Consider Superbad again: the climax involves Evan bolting in fear from his crush's drunken advances.

That approach is fundamentally at odds with the story in Nick & Norah. The two are supposed to take proactive steps toward their destinies, figuratively run into each other's arms. What Cera turns it into, instead, is a fairly run-of-the-mill rom-com with Norah as the protagonist and Nick as the "love interest." Nick isn't precisely Evan, or George Michael Bluth – the awkward silences and off-kilter verbosity seem more like an intentional part of his personality than a product of befuddlement; Nick's sense of humor rather than merely Cera's. But he's still the same kind of character Cera always plays.

Tellingly, it is no longer Nick who asks Norah to be his "five-minute girlfriend" to save face in front of his ex; now Norah makes the first move to save face in front of Nick's ex, who had been mocking her. In fact, until the very end of the film, Nick doesn't do much of anything. They don't find each other; Norah finds him, and drags him to her, kicking and screaming.

The movie is still very funny – Cera brings with him a dimension of humor that the Cohn-Levithan novel didn't dream of. His schtick is as potent and as funny as ever; it still hasn't gotten old. His reactions to people thinking that his Yugo is a taxi? Awesome. But that stuff comes at the expense of the story's emotional core.

Here's the problem, and what I didn't realize when I wrote the first column: for Michael Cera, "range" may be irrelevant. Right now, he's much more of a comic than an actor. He's a brilliant comic, but his style doesn't fit every project. The price of fame may be that agents and producers will try to shoehorn him where he doesn't belong – and, most likely, where he doesn't want to be. He needs to watch out, as do directors and screenwriters. Nick & Norah's Infinite Playlist could have resembled another Before Sunrise. Instead it's closer to a PG-13 Superbad.