I think this idea could be expanded upon, maybe in a turn-based manner somewhat akin to the old Worms games. It seems easy to spam the left quarter-to-third of the screen with short button presses (maybe have the catapult reload with a cooldown?).
As it is, I feel it's a bit lacking in the feedback department. There are no visual or audio cues to determine how far a shot will travel, leading to a rhythm- or memory based playstyle which, to me, turned out a bit less relaxing than could have been.
I think the description is missing something like "as you can" in the first line.
Anyway, it feels like one could do a lot with the presented concept!