Just some new comments:
Some places are "invisible" because you can just jump high enough to reach the spot.
Some apples are just there for backtracking (feels like a chore).
I think you should at least in the first few levels make the apples "guide" you to the exit not just spam them everywhere on the screen instead of breaking the immersion with arrows and/or pointers.
Very nice graphics.
Should do something about the graphics in the titlescreen/menu?
When you get the key, please let us pick up the balloon at the same time.
New game mechanic: While holding ballon you can "glide" when falling.
These are just some minor improvements that I am sure you are going to do something about sooner or later, but just wanted to let you know ;)