-Can't see what you're aiming at.
-No map to show you where the targets are in the first place.
-Misses mean climbing back up all over again (ugh).
-"Advanced" moves are extremely difficult to time correctly.
I like the concept of using the stylus to "fling" your guy around with rubber-band physics. Unfortunately, most of the "stars" you're aiming at to get points are going to be off-screen, so you're forced to aim for them by memory, and to fling yourself all over the place trying to find them in the first place. There are also lots of hazards off-screen (like spikes on the walls), so getting "good" at the game means lots of repetition and memorization. Also, most misses mean having to fling several times to climb back up for another try. The advanced techniques require split-second timing when the screen motion is very fast (faster than the DS can handle smoothly).
With a map showing targets and a way to "zoom out", this game would be MUCH better.