Nobody wants to hear that something they have spent so long working at isn't the best book ever, but let's face it out of all the books in this world only one can have the title of best book ever and chances are it isn't going to be me or anyone else I know. Probably not even anyone else living. But everyone can have his or her best book, and the only way to get it is to take a few hard punches, look at what you have with a different perspective and start improving it. People who love you generally don't want to hurt your feelings, but it doesn't do anyone, whether it be a writer, or a skater, or a football player, or a math student, to be told that their mediocre effort is brilliant and wonderful and nothing needs to be changed. Critique propels greatness. The Olympics just wrapped up, and I bet every single athlete had a coach who drove them every day to be better. That spin was awful, do it again. You're not fast enough, try it this way. You're not strong enough, you need to work harder. And it's the same with writing.
If you have a manuscript, or any other project that you are working on, don't be afraid of criticism, it is what will make you better.