THE FAULT IN OUR STARS The kids are all right (except for the cancer thing).

IT'S BEST NOT TO COMPARE movies too closely to the novels they're based on—stories can and should be told differently in different mediums, right? Dancing about architecture and all that.

Comparisons are unavoidable, though, when instead of adapting a novel, a filmmaker tries to make a perfect carbon copy.

John Green's The Fault in Our Stars is one of the most popular young adult novels of the last several years, and one of the rare YA titles to make serious headway with adults as well. Through the lens of two love-struck teenagers—both of whom happen to have cancer—the novel addresses mortality and illness with clarity, humor, and depth. (Seriously: Give it a read, snooty grownups.)

In a word, the source material is terrific—so it's understandable that in adapting Green's novel for the screen, director Josh Boone and screenwriters Scott Neustadter and Michael H. Weber hewed closely to it. In some regards, their respect for the novel pays off: The story of fierce Hazel (Shailene Woodley) and her manic pixie dream boyfriend Augustus (Ansel Elgort), who meet in a support group for teens with cancer, is deeply romantic. They're perfectly star-crossed: Hazel is a cancer-filled grenade, she tells Augustus, trying to resist his affections. She's okay for now, but only just. Will they or won't they? And Green's notion of a band of irreverent, outsider teens (with cancer!) translates almost better to film, calling to mind the cinematic precedents set by any John Hughes movie.

But other elements of the book probably should've stayed on the page. Green's novel builds its own rich internal mythology, complete with original source texts—Hazel's favorite book, An Imperial Affliction, is about a young woman with leukemia; it ends, abruptly and in midsentence, with the death of the narrator. Hazel is obsessed with the book, which speaks strongly to her own experience, and she's determined to find out what happened to the rest of its characters after the death of the narrator.

In Green's novel, it's clear that her obsession with the ending of An Imperial Affliction stems from wondering how her own family will fare after her death. In the film, though, the significance of Affliction is only glancingly addressed—it serves mostly as a means to shoehorn in a trip to Amsterdam, where Hazel and Gus track down the book's author. The fizzy, romantic scenes from their trip are delightful—these actors are unspeakably adorable—but heavier scenes that work well in the book, like a visit to the Anne Frank House, are more strange than illuminating.

Not to be too down on the film, because there's plenty that's good about it: This is a teen movie that's frank and non-schmaltzy about death. It's openly contemptuous of many of the platitudes that surround the sick and the dying, while also recognizing the need for compassion, and the kindness of a well-timed, consoling lie. It's a movie where two teenagers have sex, and no one is judgmental about it; Shailene Woodley's Hazel sets a cinematic high watermark for complex, fully realized teen-girl characters. It's funny. It's well acted. And it'll make you cry.