Wow, that graphics! I loved the monsters! The font clashed a bit with the rest of the style, but that's the only thing I didn't like, visually. The overall look and mood was amazing. Nice level design, too.
The controls don't feel right, though. I don't know if it's because the web version is a bit slower, but the movement and jump feel very indirect. In my opinion you could have made the jump definetly faster and with some acceleration at the end. On the contrary, the fact that the balls you shot were bouncy and slow made them more fun.
Also, consider sticking to common control schemes, like left mouse button to shot - space to jump - wasd to move. I think it would be more intuitive for your players, considering that in a jam you're referring to an audience of gamers.
Still, I enjoyed going through the levels! Good job! And I hope this feedback was useful :)