1. 10 very satisfying :D
2. 10/10 very simple!
3. not bored, but since there is no objective and it is instantly clear I did like 10 - 20
4. sounds - 10/10 :) regarding the visuals - I would love to see more dynamics of otter swimming :)
5. Some notes:
- It feels like there is a lot of oysters from the start - I don't think that is necessary, the amount can be increased with time.
- some oysters are swimming under the otter, I would leave them swimming around the otter instead.
- I think some oysters could be harder to open - would be fun :)
- the UI showing the oysters limit - I would place it somewhere else or even removed it, maybe add some mechanics showing "too many"
I think my main suggestion would be to add some objective, maybe player can collect something from the oysters.