In fact, 21 Jump Street's script (from a story by co-star Jonah Hill, with the script by Michael Bacall) straight up acknowledges the flimsiness and implausibility of mining the same material that made Johnny Depp a household name in a never-anything-below-yelling speech by Ice Cube's Captain Dickson character.
Yes, 21 Jump Street is about a pair of mismatched cops returning to high school to bust a synthetic drug ring, but the hook of the movie, what makes it work so well and actually allows the characters to develop during the course of the plot, is that instead of slipping back into the nerd/jock roles they had in high school, Hill and Channing Tatum's Schmidt and Jenko find out that the social terrain is vastly different. Indifferent bad boy tough guys are on the outside while socially conscious double-strap backpack-wearing sensitive guys are in.
In an opening flashback sequence set in 2005 (incongruously set to "The Real Slim Shady," although technically the song was rereleased in an '05 compilation), we see Schmidt for the first time, an awkward, bleach-blonde loser with braces, while Jenko was the letter jacket wearing jock. Schmidt in high school wasn't able to get anywhere with the girls while Jenko wasn't getting anywhere with his grades. The next time we see them together, it's at the police academy, where they could fall back into the pattern of bully/bullied but strike up a friendship as Jenko helps Schmidt get fit while Schmidt helps Jenko pass his exams.
Still, the mean streets aren't for them, and after a bike patrol drug bust goes wrong, they're knocked down the the Jump Street program, which places young-looking cops into high schools to investigate crimes.
Hill and Tatum have an easy rapport and the characters seem to have genuine affection for one another. Forget tv-to-film comedies, many comedy scripts and their performers fail to figure out how to do this.
When the duo head back to high school, inverting their roles also gives the movie focus. Now Schmidt isn't the focused, smart cop: he's the cool kid who's a little too popular for his longtime friend. Now Jenko is the off-putting outsider with too much bro energy who has to hang with the science club set (although those kids are secretly cool; they know how to blow stuff up).
If I've dwelled on the dramatic arc of the characters a lot, it's because structurally, the movie works so well. But that would be ignoring how genuinely funny the movie is. Most of the humor comes from the manic chaos from Jenko and Schmidt, two grown-ass men, wreaking havoc, abusing their authority, and generally reverting back to their teenage selves. Then you've got supporting actors like Rob Riggle as an amped-up coach and Chris Parnell as a drama teacher keeping the action moving (although Elie Kemper's science teacher with the hots for Jenko is a running gag that goes nowhere).
Did I mention the car chase involving multiple car requisitions? Or that Jenko and Schmidt have to move in with Schmidt's parents to maintain their cover ID? Korean Jesus? Or Schmidt's difficulty navigating the more laissez faire sexual attitudes of modern high school students? Or the Peter Pan fight? 21 Jump Street is full of well-executed moments like these and the best part is that they never overstay their welcome while also keeping the plot moving.
By the way, if you want one of the movie's funnier bits left unspoiled, hold off on reading the special features section and don't navigate to that section of the Blu-ray menu before watching the film.
You've got some good stuff here including the feature length commentary and a couple of featurettes. I still don't know who likes gag reels but you got one as well as 20 deleted scenes, along with separate spotlight pieces on stars Rob Riggle and Ice Cube. Finally, you can catch Johnny Depp on set as he preps for his cameo.
Holy crap, looking at the IMDB entry for the movie, I see that Richard Grieco also had a cameo in the movie.
21 Jump Street is available now on DVD, Blu-ray, and VOD.