Had fun with it! Once you get the hang of it, it's a neat implementation of the grappling hook.
The game is gorgeous, I absolutely loved the background and the effects when the bats die!
The music is cool though I found the shotgun blast a bit too underwhelming, it lacks that punch. You feel the character moving but the sound doesn't quite translate that to me.
I downloaded the game after trying a bit on my browser (it's Firefox) and finding it too laggy. It's kinda rare to download a game that is playable on a browser, so I think that's a good signal! Also, that's probably on the browser version but the animations showing the grappling hook in action before playing were just black blocks in my tutorial.
Somehow I managed to get over 1000 points easily on the browser, though I barely got very far up. On the windows build I managed to play for many minutes but just got 1748 points. I didn't understand if shooting the ghosts counted, I did a lot of it on the browser version since I barely could go up. Or perhaps there's some WebGL shenanigans at work, and the vertical space of the browser version counts in a weird way?
The interactions with the bats were a pain, sometimes they'd be right in front of my character and my shots just passed through 'em. Their hitboxes seemed a bit wonky. By shooting from afar it was absolutely easier to kill.
I might have missed it, but I didn't find something that showed me a platform was "reachable" so many times I'd just blindly fire the grappling hook hoping the distance was okay. Sometimes it wasn't and I'd panic a bit. I also didn't understand the boosting mechanic, but I guess that's on me! Does it depend on the distance of the grappling hook or is it some sort of cooldown timer?
All in all, I had fun and it was a neat application of a gun with multiple functions! Congratulations!