I agree with Julily, Ash. Very well worded and helpful. Yes, you gave them a LOT to work on...but...if they take your advice, they can completely turn the story around. I know that I would want that kind of concrit if I wrote something that...sucked. lol.
So don't worry about sounding jerky....lol. If they know how to handle the criticism just meant to help them out....then they wont take any offense.