Harry is parentless. This proves bad on few levels. In the material world, Harry didn't know what the fairy tale book in the the story had anything to do with their quest. And this was really bad, because it took them half of the book to find out about them. And I like how Hermione is the one who figured it out, and she's muggle born!!!!!
On the other hand, Harry lacks the parental guidance he needs to be a grownup. His parents would have showed him, but without them he's stuck in the 11 year old mind state he had when he entered Hogwarts. Not good! He's impulsive, but this brings me to another theme I noticed.
Harry's dad's friends, such as Lupin and Sirius, are like fathers to him. They lived on, so that he could grow up learning lessons from each one of them. The only issue is they all died, so he is basically tight, because he had a father figure, and he got deaded(killed) in the battle for Hogwarts.