This lends itself well to being a good simple mobile game. The beach feel was cute and worked well. The graphics and audio were nice and fit the feel of the game.
The SFX for collecting the seashells was a little quiet compared to the other ones; balancing the sounds a bit more would be nice. It would also be nice if there was a different SFX for your player losing a star and the rocks hitting something to help convey information.
I liked the tutorial. It did a good job of giving the basics.
It took me a bit to figure out how the stars work. I acknowledged that collecting the seashells made the seashells number increase, and started actively looking for stars and shields. When I didn't see any stars, I realized it was probably connected to moving the sandals when in the wrong direction or getting hit by a crab. The shields took me a little longer to figure out. I went through a few levels before clicking on the crossed swords and learning they were a shop. I had thought the swords were a combat mode or a leaderboard, not a shop. You might want to change the icon to a dollar sign, a building, or similar to better convey what it is.
Having a face paced, endless mode and a slower paced, puzzle-like mode was a nice touch. I thought they both worked pretty well.