Idk about the theme. It looks like you just put the storyline about the jellyfish. It's pretty creative ngl, but it doesn't affect the gameplay at all :(
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About the gameplay: the game is super catchy, I've spent a lot of time playing it(made it to the wave 35 yay), however, correct me if i'm mistaking, but after wave ~25 jellyfishes are fast as hell and the only useful "tower" is a turtle, other ones just can't handle it. So gameplay becomes placing as many turtles as you can until jellyfishes just break them all. It'd be nice to balance this part a bit, but in overall it's super fun to play!