Great concept with a lot of cool details other commenter mentioned, but just the basic feel of moving around and jumping, among other things, make it really hard to play and enjoy. In particular the acceleration/deceleration bothered me quite a bit, the overall moving aroudn just felt jerky and awkward.
IMO the first thing to nail with this kind of game is moving and jumping, and just a tiny bit more feedback for player actions and to communicate state - e.g. basic sounds for shooting, jumping, reloading, etc go a REALLY long way, a flash when something gets hit and takes damage, and a health bar of some kind!
I didn't mind the controls, they made sense for keyboard-only play.
It was fun to discover picking up multiple guns, playing around with the enemy AI (how they jump up and down from platforms, simple but effective), and discovering you can shoot upward (with an animation!) after a few attempts.
I persevered until I got to 34 enemies, which I thought would be impossible after my first couple of attempts, so there's definitely a skill curve.
Points for style!