I haven't finished this yet (the first boss kicked my butt), but I plan to come back! You did a great job teaching the player mechanics like killing the unkillable crabs via pushing blocks on them, and all the puzzles I've encountered through the first boss have been well conveyed and thoughtfully done. Also there is just the right amount of flounce to Sarah's hair, which makes for a fun-to-walk-around sprite. My only criticism is that Sarah's hurtbox seems a tad large in the upward direction, makes it hard to hit enemies from below with your sword.
(Edited to add: I love the crab sprites so much!)