The act of taking past TV shows with any semblance of name value and updating them for the big screen has become so commonplace these days that it barely makes any impression at all on audiences who have been ground into submission. Of course, in actuality it is but a flimsy excuse for Hollywood studios to steal old, identifiable, potentially lucrative brands in lieu of having to think of original ideas, and "21 Jump Street" deserves credit for openly acknowledging this in an early scene that acerbically comments on its own derivativeness. A comedic, hard-R take on the 1980s one-hour drama that made a name for Johnny Depp, the film stars the game pairing of Channing Tatum (2012's "The Vow") and a slimmed-down Jonah Hill (2011's "The Sitter") as an odd couple of youthful-looking police officers going undercover as high school students to infiltrate a drug ring. Shades of 1999's "Never Been Kissed" follow as the guys get to relive their teen experiences with starkly different results, realizing along the way that they have grown into better people no longer chained to the scars of their adolescence. None of it rewrites genre rules or moves beyond the predictable, but directors Phil Lord and Christopher Miller (2009's "Cloudy with a Chance of Meatballs") enlighten the proceedings with frequently perverse high energy and a dab of sweetness.

Seven years ago, Morton Schmidt (Jonah Hill) was a hopelessly tongue-tied 17-year-old with a bleached hair job that got him nicknamed "The Not-So-Slim Shady." Greg Jenko (Channing Tatum) was a bit more popular, but an academic failure, barely squeaking by to graduation. Now in their mid-twenties, these two opposites meet up again at the police academy and fast become friends. Following a botched park arrest that leaves them outcasts, Captain Dickson (Ice Cube) sentences Schmidt and Jenko to 21 Jump Street, a gathering at the beaten-down Aroma of Christ Church where they are handed a last-ditch chance to redeem themselves on the force. Their mission: to go undercover as high school students—and brothers—Doug and Brad while investigating the rampant use of a dangerous hallucinogenic called H.F.S. By getting in tight with dealer and classmate Eric (Dave Franco), it will only be a matter of time before they find the supplier.

Up until now, Michael Bacall's screenplays have been an epileptic study in mixed messages. Is he a lightning-fast talent of quips and heart due to 2010's "Scott Pilgrim vs. the World," or is he a loathsome cockroach after 2012's despicable "Project X?" Maybe "21 Jump Street" is the closest to Bacall's actual movie taste, a happy medium of easy-to-watch mainstream fluff and coarser gags for which its MPAA rating is bountifully earned. A cross between a ribald teen comedy and an action pic with a particularly ample car chase near the end, the film ultimately earns most of its good will with a portrait of two men realizing just how much things have changed in the years since their own high school days. In a name mix-up, the daft Jenko finds himself posing as Brad, the brainy one with a penchant for AP chemistry, while Schmidt embodies Doug, getting saddled with track meets, drama class and the lead role in the school's upcoming production of "Peter Pan." As Jenko quickly learns that his glory days may be over, Schmidt, bettered by more experience and confidence in his own life, wins over the student body, successfully befriends the drug-dealing Eric, and even works up the courage to ask the fetching Molly (Brie Larson) to the Prom. To add to the illusion, the two of them move in with Schmidt's overbearing parents (Caroline Aaron and Joe Chrest) and, true to form, throw a big blowout the weekend they go out of town. This scene, full of care-free freedom, unspoken nostalgia and LMFAO's "Party Rock Anthem," betters in five minutes what the far-fetched, just plain ugly portrayal in "Project X" couldn't achieve in an hour and a half.

The baser material is hit-and-miss (we could probably do without the castration), and so is the rather transparent narrative that makes the identity of the drug supplier a question the viewer doesn't particularly have any stake in getting answered (that said, when it comes, it's a humdinger). Subplots, like Jenko finding acceptance in three unpopular science geeks—the very people he once ridiculed—and flustered chemistry teacher Ms. Griggs (Ellie Kemper) barely able to keep her attraction to him in check, are set up and then peter out rather than reach a conclusion. Schmidt's side of the story is a bit more focused, the relationship between him and Molly humbly likable and his acceptance into the "in"-crowd welcomely non-stereotypical. Soon, Schmidt is being taken over by his Doug persona to the point where he starts to not recognize himself. Neither does Jenko, who tries to warn him. "You're in too deep," he says. "Yesterday I found a college application on your desk."

"21 Jump Street" is loose and meandering, but it also knows how and when to entertain. By taking the general premise of its source material, but otherwise doing its own thing, the film is able to make a name for itself beyond the title. For their parts, Jonah Hill and Channing Tatum are terrific, both of them at ease doing comedy and playing off one another. Hill lost a lot of weight for this role, and he proves once and for all that the size of a person isn't what makes him or her funny as long as they're truly gifted. As for Tatum, he is growing leaps and bounds with each new film. Once stiff and bland, he has grown into a charismatic, even powerful leading man. Brie Larson (2011's "Tanner Hall") and Dave Franco (2011's "Fright Night") make the most of their screen time as the independent Molly and sketchy Eric, while Ellie Kemper (2011's "Bridesmaids") is too brazenly amusing for such a scant part as the libidinous Ms. Griggs. Her kooky character is one that ought to have been further fleshed out. "21 Jump Street" erupts into violence by the finale, some of it unappealing, but it's a means to an end in a free-for-all action-comedy that works for what it is and even hits a few notes of honesty about growing up along the way. Just don't expect any of it to stick too hard after the fact.