The concept is creative. Not the first one I have seen, but I will give five star for innovation.
The gameplay unfortunately gets monotonous really quickly. From beginning to end it's basically the same thing. One of the main problems I see is that how the main mechanics of the game is puzzle-ish with the window resizing mechanics and all, and yet the difficulty of the game relies too heavily on the amount of enemies - that unfortunately doesn't accentuate that core mechanic. I think you should have added for example moving platforms, some block types that moves with the screen resize, or make the enemies more affected by the resizing mechanics one way or another (e.g. add new enemies that are affected).
Another big problem is how linear the level design is. In each stage it is so obvious what to do. And then also there is also how plain the level design is... I have hard time describing what I mean exactly but... it is too square-ish perhaps..? Especially when the blocks are dirt and grass, I think the stage design should be a little bit more... curvy perhaps? I realize that with that mechanic making the stage slightly curvy would pose some problems though. Maybe the game would fit better if the setting is instead inside a laboratory or something?
The graphics itself is adequate. It can be better, but I think this is good enough. The SFX and music also fit the game well.
Overall it has got potential. I more or less enjoyed it, but there are certainly rooms to be improved. The criticisms are meant to be constructive, and I hope it helps and doesn't offend you. Good work, and I hope you will make better games in the future :)