I played it many times over, definitely not trying to speedrun it or anything.
The crystal key hitbox is infuriatingly bizarre, 90% of my resets were because of them not being picked up.
The visual theme of the game so far seems good, I like the overall look of it, but lighting could be improved a little more. Not necessarily make it brighter perse, but make the dark areas less black.
The environment is walled off in odd ways, invisible barriers make exploration impossible, which I suppose it intentional with a linear style game, but cmon man let me look around and not be blocked by something that isn't even there.
The movement of the player character is responsive and good, just wish it didn't feel like I was on the moon as much.
Boss fight is... tragic. You just stand there and hold left click until its dead. The generic enemies are also somewhat mediocre, but it feels more like they're just very basic enemies put there so theres something to shoot at moreso than what the actual enemies would be like.
The concept of puzzle being used is very open. I'm not sure I'd call collecting keys and trying to nail targets in a timed event puzzles. If you want to actually market it as a puzzle game, perhaps making use of the player's wall for puzzles would be a good option? Currently it serves no real purpose.
Overall, a decent prototype for what the game could become, but even as a proof of concept it needs some baseline work to properly convey what it is you intend to make.