If there's one thing that stands out to me in a great book or television show it is awesome characters. In my mind, these personalities (or lack there of...) can make or break a show. You can have awesome plot twists, terrific writing but if you don't have characters that people connect with, it falls flat.
We like variety, diverse and dynamic characters. As I've said before, personalities that jump off the page because they seem so real, so interesting; they're the people you want to learn more about with every chapter or in the case of a television show, each episode.
Characters should grow especially if you have them in a series. Just like everyday people, it seems a bit unusual to not see growth or at the very least, a change in opinion over time. As you learn about the characters, they're often learning about themselves. Even more interestingly, the characters you're drawn to might also be telling you something about yourself.