Hello, I am not an expert in level design, but I can try to help with polish. So about your game, I really like the uniqueness and the art style.
To add more polish, first thing that would have been really nice would have been sounds. For example, the player shoots the web, hears a "THWIP", that's instant feedback for the player.
Secondly, some more animations, especially for a 2D platformer go a long way (even something as simple as the character squishing a bit when landing.
Also, a lot of developers use techniques like Coyote Time, Jump Buffer, Increasing Player's acceleration when falling downwards and so on to improve how it feels to control the player. Those topics are something you should definitely look into since they are too much to go into a comment!
Best of luck!