Issues with difficulty/graphics, but a good effort
The music is lovely, but there's issues with the difficulty and the graphics.
If you're going to do silhouette graphics, you've got to make it really interesting to look at. Give us more shapes of things to enjoy while we're looking at the game. Otherwise it gets pretty bland, and when you're playing a game like this where you'll be replaying parts over and over until you get it right, there should at least be some really yummy graphics to look at. Examples of where this is done right in your game is with the grass on the cliffs, and the spikey enemies. Those are some interesting shapes!
I'd also suggest something other than white on black. It looks nice for a while, but it hurts the eyes.
Admittedly, I didn't try easy mode, so the following is all based on my experience playing the default mode. This was frustratingly hard in several places, and the problem always had to do with judging how to jump on and off inclined platforms.
The worst was one part after the spaceship crash area, where you had to jump across 3 or 4 flat platforms, land on a platform with a sharp incline downwards then gradual incline downwords, somehow propel yourself with enough momentum to the next flat platform, then back up and jump up to the next area where the checkpoint was. This was ridiculously hard. I tried this over and over, dying at least 50 times before I finally did it. I don't know how I didn't give up and just ragequit.
To keep the difficulty at a level where it's both fun and challenging, I'd suggest easier jumps but less checkpoints. Right now you've got lots of checkpoints to compensate for the impossible jumps, but these combine to create a really repetitive playing experience.
Having said all this, please take this as constructive criticism! I'm not just some jerk who likes badmouthing people's hard work while hiding behind the anonymity of the internet. I'm a jerk who wants to be helpful.
This is a great effort, especially for a first game by someone not familiar at all with programming. Once again, top notch music choices.