When I first heard of Randy Cunningham 9th Grade Ninja I was not impressed. The premise is basically Danny Phantom by way of American Dragon aesthetics, and when those shows were new the concept was still old. But I was completely wrong.
The show's title is also it's summary, but I'll give more detail. For 800 years Norrisville has been protected by a masked hero known as the Ninja. But unknown to the public, every four years a new hero is selected to don the mask and fight off the forces of Evil.
The strength of RC9GN is not in originality, what makes RC9GN great is execution. RC9GN was a good student, learning from cartoons who came before and using what made them work. A quick but creative transformation that can be extended but also easily be done in seconds, fluid and intense animation during show's many fights, a great sense of comedic timing, and characters (heroes and villains) that are well designed, likable, fallible, and consistent. Randy grows and learns, and the villains he fights are both hilarious and threatening. The mythos is revealed piece by piece at a slow but steady pace that feels like the characters are learning more about the past. RC9GN is like the best parts of all previous high school super hero cartoons were cherry picked and used effectively.
But RC9GN isn't devoid of creative thought. Instead of struggling to learn on his own or having some kind of mentor figure, Randy has the Ninjanomicon, a mystical book that provides knowledge and hints. Instead of just reading it Randy can literally dive into the book, his mind leaving his body while he enters a world drawn in a traditional Japanese style. But this is a textbook, and an ancient one at that, so it's covered in margin doodles and the important bits are highlighted, tips from ninjas before interacting with the Japanese art as well as popping up in combat creates this really neat feel.
Not to say the show is perfect. The villains are hilarious but completely static, it can indulge is some pretty juvenile humor that really doesn't work, and every once in a while that character animation becomes incredibly stiff and boring. Randy grows and changes but the world around him is very constant at this point, no sense of consequences or change in the world at large.
But these are small complaints, so do yourself a favor and watch RC9GN.