Hollow Floor - Demo The game has good fundamentals but it needs more meat on its bones. Here are some things I recommend before shipping on steam:
More powerups - The airwalking powerup is fun and well designed, but it alone can't carry the game. New powerups could expand on the game and make it more interesting. Movement powerups would make backtracking something the player would enjoy (this especially true for metroidvanias)
Improved player sprite - The player sprite as is functionally fine but isn't very unique or inserting to look at. I would suggest giving the legs more of a focus in the character. Another idea I had in mind is that the player sprite changes color when they use a powerup. This would be a good way to visually give direct feedback to the player without having to use up precious pixels
Enemies - The only fail state in the game so far is spikes. Spikes are fine, but they can only get you so far. Having more dynamic obstacles for the player to navigate can spice up game play and allow for better level design.
Overall the demo is perfectly fine for what it is. However, if you want the final product to last longer that an hour and have it be memorable, the game needs to evolve and give new challenges to the player. After clearing the first few rooms with the power up, the game felt to one note. Having more dynamic challenges can make this game fun and worth a price tag.