For a game made in 2 days pretty sweet
However i will still criticize a bit ;)
As others noted, the gravity is an issue. I do my gravity coding like this: The character has a vertical number, meaning the player will move up or down depending on the vertical number. The gravity is a constant -1 for any time you're not on the ground. For example, when you press jump, you get a +10. Thus you move 10 pixels up. In the next frame gravity reduces 1(since you're in the air), thus you move 9 up, in the next frame 8, 7 etc. Thus eventually you reach 0 somewhere in the air. Then gravity continues to add -1, thus you're not at -1 and move 1 down. In the next frame it adds up -2, you move 2 down, then -3, -4 etc. (it goes on forever, or until you reach a max fall speed. Like -15 or so). If you do it like that, it feels like a perfect natural jump. (Of course change the number for jump strength and gravity based on the framerate/timerate etc.)
Oh, and another platform tip: Many platformers give the player a second to press jump even after falling off a cliff. When i learned about this i thought "That's bull, if a player can't jump when on the floor then it is his own fault" however i quickly realized when making my own platformer that yes, it is indeed better to give the player a moment to react, even after falling off a floor.
In the third level though, the one where the spikes appear, it was impossible to win. It was impossible to get all the coins and not die from the spikes, as you can only move in one direction.
But like i said, i enjoyed it. And considering only 2 days, wow.