Robin, if included should be an amalgam character, with elements of both Dick Grayson and Jason Todd. Start him out as an orphan on the streets, rather than as Bruce Wayne's ward. He's inspired by Batman to take revenge against the evil around him, and does so brutally in the guise of the Red Hood. As Red Hood doesn't have any qualms about killing, an unfortunate consequence of Batman's decision to take the fall for Dent's killings. Batman goes after Red Hood, and finds about that he's only a kid, around 11-13. Instead of turning th ekid over to the police, he takes the kid into his home, and tries to teach him how to fight crime the right way.
As for villains, Riddler should be used as a string-pulling mastermind, the sort of individual that everyone works for, but no one has met. A reptation witout a face. He should be the sort of character who controls the entire playing field, but never sets foot on it. An enigma.