Nice entry! I liked the visuals, though at times they were a little unclear. I also had difficulty reading some pits, like others. I ran into a bug where after dying fighting the black box I couldn't move anymore (wasd stopping registering). I also agree with Pixxl's suggestion about introducing concepts more gradually. 

Looks good, seems to have a lot of interesting mechanics and such and seems like a metroidvania. Didn't get far as you have space for jump along with WASD for movement and a mouse for shooting and blocking. Moving right and jumping at the same time is awkward and uncomfortable for me to do with my left hand the way you have it setup. Not sure why you couldn't of just used W for jump instead.

Great game! I really liked it, but unfortunately it was a bit too buggy for me to complete it. I ended up clipping outside the world quite a bit, both when traversing the world and when restarting after death. I really feel that if you iron out some of these problems, then you'll have something really awesome!

Other general notes:

Perhaps a more gradual tutorial would be nice, where concepts and controls are introduced a bit more gradually, rather than all at once. Concepts like the inventory were a little tricky for me to grasp as well. When asked by the shop to get certain things first it wasn't really clear what they were. In the inventory and in the world they are icons, but the shop asks for them by their names, which got a bit tricky for me.

Doing things, like combat or clearing destructible walls felt great. I really like the screenshake and sound effects. It was very satisfying!

Upgrading your character to be more potent was really satisfying as well. The gameplay loop of gathering loot and then upgrading your character was really nice. Perhaps the main base should've been somewhere else in the level though? Backtracking through the mountain every time was a bit boring.

One clever thing I liked was how you introduced the destructible walls. Placing a turret on it that you instinctively try to smash was a very intuitive way to discover the breakable walls. Very nice!

I liked much of the artwork, but some of it was a little too noisy in my opinion.

Perhaps you could make it clearer where you can safely go and where a pit is deadly.

I liked the variety in the enemies. Their behaviors were nice and predictable.

I didn't understand that I could fight the black cube.. Maybe it could be made to look more enemy-like?

Some quirks I noticed:

You can heal endlessly in spawn, meaning you can be basically invulnerable in game.

The options button doesn't work, neither in the menu or in game.

If you do decide to work further on it after the jam, I'd be very interested in playing a later version with some bugs squashed!