When they tell you what they are going to do, instead of you figuring it out, that's a good sign. When their daily lives get in the way of the adventure you have put them on, that's also a good sign. (I think of Tony Soprano, he really needs to go out and clip somebody, but his wife wants him to talk to his kid who just got suspended from school.)
Confusion is another good sign. James Bond always knows what to do, but he's not exactly three dimensional.
Also, writing is a form of communication. It's only successful if people respond to it. If no one likes it, it sucks. If 11 million people spend their hard earned money on your book, you are doing something right.
The one cool thing about writing, however, is that if everyone hates it, it's still possible that years from now 11 million people will buy a copy of your book. So feedback will help you, unless of course, you are an incredible genius, so advanced that you won't be appreciated for years to come.