Couple of points here:
1 - the environment and the player kinda blend in. You can get used to it, but from the begining it is not that easy to see the ninja. Perhaps a simple outline of the main character would do the job, or play a little more with finding more matching palette
2 - the controls felt for some reason bit sharp, the character felt so fast that it was sometimes hard to navigate as I would like to. Perhaps you wanted that, but generally speaking in plarforming games I feel like better approach is to have smooth movement and hard platforming rather then having player deal with harder controls
All of this is just my point of view and a suggestion from another player. In fact I enjoyed your game and you did a really good job. I like the idea and all the sounds made a really good job here as well!