I like the visual style and Game Boy-esque color palette, but I think the controls could be more intuitive. Instead of jumping with the spacebar, you could jump with the up arrow key, and it should have the option to play with WASD, since it's more comfortable for a platformer in my opinion, and because not all keyboards have arrow keys. Gameplay-wise, I don't have much to highlight, but I did find the way you incorporated the theme of being a little rat escaping from a cat clever.