Nice little platformer, with interesting level layout.
I would suggest adding sound effects and music; in the audio department, a little can go a long way to help the game world feel alive.
Also, I could not figure out what was making me weak every so often--the heart display in the top left corner never diminished.
Finally, please double-check the collision on the platforms. I frequently experienced a collision issue that significantly impeded my progress. I kept falling into the side of the platforms. From this position, I could not jump (presumably because the player is not considered "grounded").
For your convenience, I'm pasting a screenshot of the issue below.
