Okay, I just finished it. I have to say, I can see the potential here. I like the idea that you have to change the size in order to fit through different spaces. This could lead to some really interesting level design. I also like the 2.5D aesthetic.
That being said, this is obviously only a prototype, and there are definitely a lot of things missing, like sound, more art, etc.
But this is a good start. I am interested to see where you are going from here. Good job!