Definitely a cool gameplay concept, and the music and artwork are great, but I honestly would have liked it better without the rhythm aspect (or if it just moved the characters in beat increments, but didn't actually require timed inputs).
The grapple has some issues beyond just firing and moving, as sometimes I'd be standing perfectly still but the grapple would fire in the complete opposite direction of where I was facing. And I feel like the retracting mechanic hurt me more than it helped, because I'd often try to hit an enemy but accidentally press the button twice, or try to attack again too soon, and retract before actually getting the hit.
The game might take 11 minutes to beat for the developer, but for me it took several attempts to just get a sense of the game mechanics and the map layout, another one to discover that I needed to actually kill enemies, and several more to figure out some semblance of a route that would let me get enough kills on the way to the exit. So that's already many times 11 minutes, all just to get mobbed in the last room and die every time.
(I don't know if the timer actually means anything, as I reached 0 a few times and nothing seemed to happen, but I sure hope it doesn't because getting through all of that just to get a bad ending would be terrible.)
I can definitely admire the guts to go with such a niche genre, but sadly for me it was too much to go through without a checkpoint. Still, the concept is neat and there's definitely material for a really good game here with some more forgiving mechanics, so good luck if you choose to update it further!