This was an interesting concept. Felt like it could use a little more polish, but that should come with time and experience. Heads up for people trying to play this: I had issues getting the game to work for me with Firefox, but it worked fine in Chrome, so keep that in mind.
I agree with other people's comments on the controls being an issue. In a case like this, I'd say the best thing to do is take a "more is better" approach. You can keep the arrow keys for movement, but also have WASD control movement. There isn't much reason to not let players use whichever they want. Similarly, you can all pressing up (or W for WASD) to jump, as that's still fairly popular. I'm also not sure the purpose of letting players aim with the mouse, considering that pretty much everything you can shoot is on the same elevation as the player at some point. I'd also suggest looking again at your hitboxes. There was one part (level 2 I think) where it visually looked like there was ample room on the other side of an enemy, but the game disagreed. In general, it's better to have the hitboxes be a little smaller than visually indicated that a little larger, so I'd keep that in mind. Additionally, it would be nice if only the bottom side of the crushers hurt the player, as I was not expecting to be hurt by every side of it. (at that same level, my second thought after realized I couldn't fit on the other side was to jump on top of it, which didn't work either).
Overall, a good first game (at least from what I see here on itch), but looks like it could have used a little more playtesting and refinement.