Simple, to the bone gameplay, with bright colors and music which actually fits with the whole atmosphere. This game appeals to most audiences I think. Its addictive and very fun to play :)
However, nothing is perfect, and although I would love to give you 10/10, minor things stop me. The controls suit the theme of the game brilliantly, they help you to fly from one part of the screen to the other with great speed, but they conflict with the gameplay. Its like that old saying about a bull being in a china shop, except with jelly and spikes XD Its cool for the first few levels, but during the later ones, it can annoy you. Im probably over-reacting about this, but im writing this while being stuck on a level, what do you expect :)
As csdthegreat said, a twist, something new to add the the gameplay would be interesting. There are many ways in which you could transform the jelly ect. Maybe even add multiple difficulties, level creator, and upgrades? But don't over complicate things, keep it simple, with something to freshen it up.
Anyway, its really good, its hard to dislike this game. Well done on making it, and I shall be hoping for a sequel ^-^