1. It feels very satisfying (10/10). The crisp sound design makes it feel very responsive.
2. Yes, it is quite easy to understand.
3. 130+
4. Yes, it would probably be even better if it had some animation.
5. It is not frustrating. However, I noticed the oysters appear and disappear right at the border, so I can see them "popping" in and out. Maybe make them appear and disappear slightly outside the camera view so players can't see that happen.
It's a very cute idea with great potential. I’m looking forward to seeing how you continue developing this game!