Interesting stuff! I have some questions though:

- I am having a bit of trouble with the Guide Arrow [Loop] rules. Is the following a correct paraphrase?

Shade some empty cells so that no two shaded cells are orthogonally adjacent and the remaining unshaded cells form one orthogonally connected area, which contains exactly one loop. (A 2x2 square of cells is considered a loop.) Cells with stars must be unshaded and part of the loop. Cells with arrows must be unshaded, but not on the loop. An arrow indicates the only direction in which one could begin a path to the loop without going through a shaded cell or backtracking.

- For the Water Walk [Isowatari] example, the Isowatari part of the puzzle is solvable without any deductions from the Water Walk part. Is this necessarily true for the contest puzzles as well? (I'm guessing not, but...)