Oh man, I really liked this one! Gameplay-wise, it was incredibly satisfying timing the jumps in such a way that I would graze the person I want to hit without touching the ceiling/floor near them, so that I could preserve my note for as long as possible and get more people during the strum.
My first attempt was 3 strums 56 echoes. Knowing the mechanics and general placements of the people, I tried again for a better score, and got 2 strums 33 echoes :)
The only feedback I have is general QoL stuff, like a main menu, the ability to pause/quit the game, and maybe a slider for the overall volume of the game. Though, given that you're so new to game design, I'd imagine you had a lot of other concerns on your plate, haha.