We apologise for the late feedback:

I like explosion magic! This will be a fun game once you finish it. I hope that you are able to continue working on it and complete it. I really do like the concept of charging your explosion and giving it different effects as you level up. The various different upgrades are interesting and feel good. There are enough different types of upgrades to feel like it's not too simple, and the upgrades are absolutely noticable. The spawn location of the mobs in the center of the map can make the gameplay a bit difficult if you get caught in the spawn when the mobs appear and they kill you basically immediately. Adding random spawn locations within a certain distance of the character would be better, or random location off-screen. The lack of assets does make the hurtbox of the character along with the hitbox and hurtbox of the mobs difficult to feel/notice. I feel like this will get better as you add more graphics. I also suggest that you add an option to use other keys or the mouse to charge the explosion. If you could add a ghost outline of the potential explosion while charging, that would also be neat.

Your GDD is pretty bare-bones as you yourself admitted. Next time, focus on the GDD first as it will be your guide to your goals and expectations for yourself on development and design. This will help you in the future with any other games you choose to make. Adding the art design, UI wireframes, music, theme, aesthetics, and all the other things you'd expect in a GDD would also be good.

Even with the setbacks and constraints you had, this game was still fun and is absolutely a great place to start from.

Honestly had fun with this. Beside the ui and stage design, the animation carries this game. Squash and stretch goes a long way! Upgrades are cool, just wish they came more often. The only major suggestion I have is make the game full screen.