Hamlet is very much about the inner struggle faced by the title character as he contemplates his father's ghost's wish that Hamlet kill his uncle to avenge his father. Closer to our lives than we wish to admit, Hamlet is a well-rounded, thoughtful character despite his whining: he's learning to think for himself. He questions what his father's ghost wants him to do. The whole play is literally him grasping at his conflicting emotions. It's a theme that readers of any age can appreciate: it asks us why we do what we do. 
 I've seen the version with David Tennant as Hamlet - stunning. There's a reason why plays are meant to be seen.