In a nut shell
Morton Schmidt (Johan Hill) and Greg Jenko (Channing Tatum) are former classmates from high school - the first a nerd, the second a jock - who meet again at police academy. There they end up becoming friends while helping each other with their weaknesses (study/physical activity) and graduate as partners. To their disappointment they are assigned to park patrol, but it gets better when they spot a group of One Percenters and arrest their leader. However, he gets released because Jenko forgot to read him his rights and the partners are reassigned to a revived speciality division on 21 Jump Street. Here Captain Dickson (Ice Cube) explains that their division specializes in infiltrating high schools and that Schmidt and Jenko are assigned to stop a new synthethic drug from spreading to other schools by finding the supplier. In order to do so, the partners go undercover as brothers, living with Schmidts parents. Mistake number one? Jenko accidentally switches their given identities and they get each others' classes, leaving them out of their comfort zone.
High school turned upside down
What makes this movie work is the satire. The makers aren't afraid to use the concept from the series and do anything with it. In a few years everything in high school has changed. When Jenko shows Schmidt how to be cool, he makes fun of someone else. But, that right there, makes him unpopular. He calls a kid gay and the popular kids defend their gay friend. It's not cool anymore to make fun of people who are gay or simply be mean (there might be a lesson there!). Oh, and btw the humanitarians who want to save the world? They are cool now. The environment is important. That's what it's all about! Safe to say that cool kids have changed and Schmidt and Jenko have to give it their best shot to blend in. Or have they? Because as it turns out, the popular guy Eric (Dave Franco) is the one with the drugs.
Is the world turned upside down in a few years? Maybe. Yes, the popular guy has got it all wrong in this one and the geek turns out to be cool. They both make friends and need to deal with 'peer pressure'. And epiphany: they start to understand each other better by walking in each others shoes (that's never been done before!). The weird thing is that it does work. Hill and Channing both play their parts and the funniest moments are the ones that aren't so stereotypical (like Schmidt's Peter Pan audition on drugs).
The high school drama
What bugs is the cliches. Yes, they are called that for a reason, but still. Do you not know from the beginning that these new found friends will eventually have a fight? Yes. And is it a suprise when right in time they will help each other out again? No. It's expected and if you expect it, you will less likely be annoyed by it. But it does take a lot of fun out of it, because you know what is going to happen.
All in all it's a fun movie. Not entirely original, but the difference is that they know that. That's why they take the risk of using that in satire. The drug trip is irritating, but it plays a part in the story, so it can be overlooked. And while Jonah Hill and Channing Tatum don't look like teenagers, they play the teen drama very well (and it's fun to watch - besides, they also make jokes about that ;-) ). Even better is the little gift to the audience who have seen the original series, namely the moment where Tom and Doug (Johnny Depp and Peter DeLuise, who play the main characters in the original series) show up. It gives it an extra layer and their roles are small, but thoughtful without drawing all the attention to themselves. Take the movie with a grain of salt and it's a very amusing movie that you can just enjoy without thinking too much.
Of course the original cannot be forgotten, so here's a little something ;-)