I think this is great so far! It was honestly pretty fun to play. I was just going to check out the game, but I ended up playing several times.
I encountered two bugs I think?
1: The game suddenly just froze. I don't know how or why, but it was when the boss reached 20% health.
2: I couldn't level up past level 5 (I believe), although this might just be because you haven't added content past level 5
I also had a few other kinds of issues. If you don't want that kind of feedback feel free to ignore ˙ᵕ˙
1: It was a bit difficult to see when the gun is about to overheat when I was surrounded, since the gun is behind the enemies. Would it be possible to get like a tiny bit of smoke right before it overheats?
2: I had no idea what the counter in the upper left corner was. I assume you're going to make something that explains it.
3: When I picked up random cards that the enemies dropped, I didn't always have time to read them. Would it be possible to add click to dismiss or at least pause the game for a second or two to let the player read?