I'm going to be completely honest with you. My first impression of this show was "what a weird, quirky, and stupid show."
I still uphold to my initial impression, because it is weird. It's quirky. And it is wonderfully and wittingly stupid. Those qualities that first shunned me from watching the show happens to be some of the best aspects I've come to appreciate and enjoy. What I mean by wittingly stupid is that the show writers are aware of the stupidity that they've written and aren't afraid to poke fun of it within the episodes. And what seems like stupid remarks at first glance are actually well thought-out, witty lines, that it brings a certain idiotic charm to the show (yes, I use the term 'stupid' a lot, but it is very much used in an endearing way).
And this show is beyond just those three qualities I have mentioned. The art is cartoony looking because...well...this IS a cartoon, but the animation flows extremely smoothly which makes ninja fights, scarf movements, and even the way the characters bob up and down from walking great eye-candy. If you really pay attention to the background art (which is a bit hard to miss), you'll get a beautiful visual with color schemes that'll make you want to hug the artists for providing such beauty for your eyes to soak in. Each episode is fast-paced but it works really well for the show's style, and every second used is never a waste.
As for the actual plot line, I won't give anything away, but for a show that uses a lot of cliché (good vs. evil, high school hero, etc.), it brings something new, fresh, and unexpected every time, which is why this show never gets old for me (although I admit, I may be old for this show). And yes, I may be part of the older audience, but this show brings laughs and entertainment for both old and young. Enough simplistic jokes to make the kids smile, but more than enough witty banters to reel in the adults.
There is more to this show than what I've just written, but I'll let you guys watch it to see what makes Randy Cunningham: 9th Grade Ninja such a spectacular hidden gem of Disney.