This was one of the first Fox hour-long dramas, and Fox definitely wore its heart on its sleeve. Like WB now, Fox wanted to lure in a teenage audience with its good-looking young stars. Luckily for those stars, 21 Jump Street was a rather good vehicle, and stood on its own merits.
Kind of like a Mod Squad for the 80s, the "teens" in 21 Jump Street were cops. Hip cops. They would infiltrate schools, drug rings, gangs, wherever teenagers were in trouble... unlike the Mod Squad, though, the storylines were always passable, and quite often excellent. Almost every episode touched upon subjects that were taboo for the big 3 networks (and still are)- AIDS, statutory rape, drug use, abortion, child abuse- and presented it in a moralistic way, but without being maudlin.
The show kind of faltered in its last few seasons; Johnny Depp was becoming a star, and execs started pushing other "stars" into the spotlight, hoping for cash rewards and spin-offs. Richard Greico was most heavily promoted, to an audience that didn't really care. He became a teen-age heartthrob for a while, but never achieved the momentum to carry his career skyward. With this pushing of the stars, the storylines took a back seat to character preening. The end result was faltering ratings, and cancellation.
Until it became an actors' showcase, though, 21 Jump Street was probably the best drama on TV.