The movement is well implemented and offers plenty of options. The game has a save system, a shop, melee attacks, and ranged weapons.
The weapon is very satisfying to use; it could be used for puzzles, such as shooting buttons to activate platforms or doors.
The soundtrack and graphics are a good match.
I couldn't get very far in the game because I got lost on the map. My recommendation would be to use the doors cautiously, as they break the natural mental flow of a 2D map and can lead you anywhere, making it more difficult to understand a 2D map with so many doors. For example, to the left of the base you find a staircase leading to some small rooms, but I got lost because there are 10 doors in that small space, and it's impossible to predict where the door you enter will take you. In several parts, there's no need to use doors; they could place stairs or platforms instead.
The jump sound is quite irritating; it sounds like a jet propulsion effect, but the character doesn't have anything like that.
Going down a platform could be done by pressing down and jump, instead of E. I think it would feel more natural.
Grabbing a bar from above makes the character accelerate towards the bar, which creates a slightly strange snap.