What a cool take on this concept! The box switching mechanic is really well done. I like that you can see the other 'world' within the player box, and the zoom in/out is smooth. It would be nice to add WASD movement in addition to arrow keys too.
I do agree the other map within the box is a bit hard to see sometimes, maybe you could just make the level bigger since there's so much empty space around it. I'm also not sure exactly how the level ending works. I got to level 4 and was able to get the red box to touch/overlap the yellow box through jumping or falling, but the level didn't end. Also on level three, I had to try a few different iterations to progress to the next level, even though the red box was touching the yellow one in some of them (it eventually progressed by falling onto the yellow box from above).