Formidable length mars enjoyable gameplay
First of all, allow me to start with the main nagative of this game: The only reason I finished it was because of my intent to write a review for it. The game starts off quite slowly, and the level-by-level progression just seems like a mistake on your part.. That came out harshly. What I mean is that having to finish a level before moving to the next level, while acceptable, frustrates those looking for a challenge at a sooner time. Perhaps a point progression system, with X balls required to reach Y level, would have been a better choice?
Switching over to the positive side, your use of A & D was, in short, brilliant. It was the main plus of this game, and mid-jump switching made for a challenge that I personally have never experienced in gaming. I would say the same goes for the late levels with the robots; level 13 was frustrating, but in a "Later sense of accomplishment" sort of way, and I felt it was another rewarding challenge for those who kept on through the ridiculously easy parts.
I'm afraid there were more negatives, though. The portal world was unnecessarily difficult to navigate later on. (After the end, I needed to collect the one I'd missed from 8 and 10... Frustrating, and not in a good way.) The storyline was... lacking, though not much is expected from a platformer, and this caused no deduction as it was sufficient to set up the gameplay.
Graphics were impeccable, music was... honestly, the Olympics are on and it was just BG anyways, so no effect there. I considered rating this lower because it was item collection, a concept that was aggravatingly overdone in the Playstation days, but I have seen one so cleanly done in Flash so it was overruled.
There was an occasional bug where Jason wouldn't walk off the current block, but I couldn't create it when a wanted to so no help solving your problem there. Overall, your game becomes insanely addictive... sadly, it does so too late into the session to be a real classic. Your overall score is 7.75, rounded up to 8. That's good coming from me, so congratulations.