Some charming clues, as usual. I was left with a blank square in the central block of four, but then realized that 45 unclued could use two of these squares instead of one. Did anyone else have this problem? I've tried to see a pattern in the shaded squares, but although the same letter is in all the corner ones I don't see the significance. Since the instructions don't mention one I guess I was looking for something that isn't there.
Thanks, syzygy!