Like the quirky art style, and the movement mechanics were interesting. The theme was very well implemented - especially the risk and reward aspect, where you have to weigh up making the journey forward easier in exchange for more difficulty on the return.
The standard enemies are a little frustrating to deal with, though. Especially as the level design gets tighter, and it becomes virtually impossible to dodge around them for any length of time.
The level design itself is very well paced, introducing interesting new mechanics in each new area, and there's a decent amount of content, especially for a solo dev!