I love the style, spritework and charming mood of the game. The music is very nice and fitting. I think some extra clarity and action when something changes, such as a door opening or when killing an enemy could be nice. I like the teases for different abilities that you come across as you explore. The patterns of movement and attacks for enemies are nice and predictable. Sometimes the background branches would confuse me and I'd try to jump on them, perhaps a greater differentiation between foreground and background would be nice. The characters you encounter are nice and varied, although the spider boss felt a little easy while still being quite long, until I figured out just where to hit it. The controls are responsive and feel good.
The game felt very well fleshed out and well polished, and it's particularly impressive for being made in one month! Very well done.