"Invader Zim" was one of the best shows of Nickelodeon. It was dark and the humor was sarcastic and sometimes mean, but that is what make it so special. Created by Johnen Vazquez, comic book artist and author of Johnny the Homicidal Maniac, came with this incredible show. Even when the show was intended to children, the style and the character are quite interesting for teenagers and adults as well.
Basically it follows the adventures of a little and destructive alien called Zim, in his attempt to conquer the planet Earth as a "mission" (when actually the leaders send him to earth just to get rid of him) accompanied by Gir, a stupid but adorable robot as his sidekick.
Invader Zim is not like the other Nicktoons, it is more original and mature. However, like many good shows, it was canceled, without giving it a chance. What a shame (Same thing happened with "Ren & Stimpy" another good show of Nickelodeon)