The upshot of a screenwriter and/or director turning his or her own life into fiction is that the situations, conflicts and emotions depicted onscreen can often carry a more perceptible degree of authenticity. For example, Almost Famous' vivid depiction of the '70s music can undoubtedly be credited to Cameron Crowe's time as a young journalist for Rolling Stone, while Sofia Coppola's childhood spent observing her famous father and his equally famous movie star friends at least partly informs the daddy/daughter relationship in last year's underrated Somewhere. At the same time though, it's all too easy for the writer to use the cover of fiction to excise or tidy up details they'd rather not recall or, even worse, turn the reality they experienced into the stuff of pure fantasy.

For the most part, 50/50 avoids both of these traps, treating Reiser's -- or, as he's been christened in the movie, Adam Lerner's -- predicament with a combination of warm-hearted humor, raw anger and sober level-headedness that rings true. It's the little details that convince us the movie is on the level: The way Adam stops hearing anything his doctor says after he utters the word "cancer"; the frightened look in his girlfriend Rachael's (Bryce Dallas Howard) eyes when she learns their relationship is taking a turn that she's not at all prepared for; Adam's buddy Kyle's (Rogen) ham-fisted attempts to bond with his pal (and calm his own mix of raging emotions) by taking him out to get drunk and laid; and Adam pulling his overbearing mother (Anjelica Huston) close as he's being wheeled into the operating room, after spending much of the movie pushing her away. These scenes feel earnestly, nakedly honest, as if Reiser played them out precisely this way in real life and then jotted everything down word-for-word on the page.

The one notable exception to the movie's generally authentic aura is the romance Adam develops with the 24-year-old grad student that's been assigned to act as his therapist. As written by Reiser and played by Anna Kendrick, she's the kind of annoying female archetype that only exists in movies -- not the manic pixie dream girl, but the naïve, in-over-her-head flibbertigibbet who falls for our soulful hero's quiet intensity, while he's entranced by her sweetly scatter-brained ways. To be fair, it's entirely possible that Reiser really did fall for his therapist and Kendrick is performing an exacting impersonation of the woman he's with in real life, but their relationship feels calculated and contrived in a way that the rest of the film doesn't.

Worse still, it's not even particularly necessary to the movie's overarching narrative arc. A more confident film would have jettisoned the romance and kept their relationship on purely professional terms, devoting that screentime instead to fleshing out Howard's girlfriend character, who somewhat unfairly becomes the literal whore to Kendrick's idealized Madonna when she cheats on Adam just as he's starting his first round of chemotherapy. While the film at least acknowledges that Rachael's behavior is partly driven by her own insecurities, it's also needlessly unforgiving in its condemnation of her all-too-human failings. (It's worth noting that Rogen's character is never taken to task for his womanizing ways -- instead, that's meant to be part of his appeal.) More time could have been devoted to Adam and Kyle's relationship as well, less because Rogen is so hilarious in the role (though this is one of his better performances) and more due to the fact that the movie often seems poised to go beyond the typical "bromance" gags for a deeper exploration of male friendship only to repeatedly let that opportunity pass by. In fact, more than anything, Levitt's romance with Kendrick comes to feel like a way for the filmmakers to remind the audience that Adam is totally not gay for his best friend, even though he and Kyle spend an awful lot of time together.

Perhaps because this is so overtly Reiser's life story, it somehow feels churlish to dwell too much on 50/50's failings. The reality is that the cast and director Jonathan Levine do a nice job navigating the script's tricky mixture of comedy and drama and whatever laughs and tears the film wrings out of you do ultimately feel earned. And if there were still any doubts as to whether Levitt could carry a studio film, his nuanced, affecting performance here lays them to rest. Memo to future memoirists: if you're looking for the right actor to portray you in the movie version of your life, you could do far worse than Joseph Gordon-Levitt.

See more movies about terminal illness that bucked convention.

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