You brought in fandom tropes of genderbending and bodyswap and crossdressing but not in a common way. You killed Ginny but didn't dismiss or bash her. You gave Snape a chance at a new life but at great expense. You've set up an alternate canon/timeline that makes me (and a lot of people) wonder what might happen next -- can he really pull this off? does he want to? will Harry and Molly and whoever else catch him out, freak out at the deception and at Snape being Snape and at Ginny's death, too long unmourned, or, as someone else suggested in comments, will Harry figure it out himself quietly one day, and if so, will they both acknowledge it, or will they both keep the secret to themselves? -- but without needing you to write the sequel to tell us (though of course it would be wonderful).
Also, I particularly liked the line about the pond stopping Harry. A nice subtle statement about control and direction.