Fun but flawed.
This is a solid concept, and you seem to have a knack for programming and graphics; I know I didn't see any bugs. The level design is also well balanced, with a constant but gradual increase in difficulty. However, the control is unintuitive- not being able to move left or right unless you're holding down the spacebar is rather annoying and makes some areas that should be simple harder than they really are. Being able to move left/right whether flying up, down, or walking on the ground would make the game easier, more fun, and open up more possibilities for level design. Speaking of which, the game could use more levels; judging from the size of this game, you could easily fit in two dozen levels and still make it under 1000k.
What's here though is excellent. Some sort of sequel or expansion would be, quite literally, the bee's knees.