"I couldn't identify with the characters, the plot was hard to follow, and the world didn't live up to it's promise."
Ouch. Anyone else cringing at the words of this rejection? Yeah, it's pretty harsh. But it's honest. I know, because I wrote it to myself.
"Whoa! Back up. You wrote your own rejection?"
Yes, I did. It was part of a lesson in a a monster-load-of-work-but-completely-worth-it course on novel revision. After two excruciating months of reading and re-reading my rough draft without TOUCHING it (which was like dragging myself up a hill in a hailstorm by papercut-covered fingertips) and taking copious notes on what worked (10%), what didn't (90%), I could finally look at my book objectively and know what needed to be fixed and why.
Before we actually started figuring out specifically how to fix our books, the teacher made us write our own rejection letter. We had to try and see our book with the eyes of an agent or editor, and make it brutally honest. You've now read part of mine.
After the gut-twisting "Oh my gosh, I totally suck!" faded away, I knew that I wanted to make sure no editor/agent/reader ever thought that about my revised novel. It gave me direction and motivation. I now keep it where I can see it while I'm revising.
Try it. Look at your current WIP, not with the eyes the author who ripped out bits of your soul with each keystroke, but as an editor/agent who will look at it totally objectively. Then write a rejection letter--with specifics--to yourself.
Once you have it, read it over and over. Then vow to yourself that you will never actually get that letter, because you *will* fix those things.
And go do it.