For giving you something this good for free, it's almost like they're swindling themselves.
Now, Flipnote Studios isn't an RPG or anything. That's kind of obvious. It takes from the old flipbook style of animation, where a bunch of pictures are shown at a fast speed to make it look like it's moving. Flipnote Studios simplifies this. It has some tools that let you see where you last drew; things like that.
I've made some fun doodles using it, and if you have a vast imagination, you will have fun animating everything. You can even use different patterns with your lines. There's also a paint feature, which are basically blockier versions of the normal drawing tools, but they're good for certain projects.
And all of this stuff is free. Flipnote Studios costs 0 Points.
So, if you're looking for something from the DSi Store that will last and that you will enjoy, try Flipnote Studios.