Good puzzle. The last letter (the "Y" in "BY") is kind of tricky to solve logically -- it requires "second-order logic" (basically, either think ahead or use temporaries).
I agree....it's completely logical! A bit tricky at parts but there is no part of the puzzle that can't be figured out with logic. By the time you get to the word "By" it's OBVIOUS what the word is supposed to be! Thanks for the fun!! ~:)
Nice song, by the way :)