Steven Traynor isn't much of a family man. And that's putting it lightly.
First off, he's cheating on his wife like a gosh-darned fiend. To complicate matters further, he had been planning to leave her for his mistress before Will's accident forced him to refocus his energies on his family. He's still doing the dirty with said mistress, of course, but he's put his plans on hold for now.
It's also suggested that Steven wasn't very present in Will's life when Will was young. Check out this little thought bubble from his wife Camilla: "You were never really there for him. Not emotionally. You were just the absence he was always striving to impress" (8.38).
Still, Steven Traynor does a lot for his son, even if he isn't there for him as much as Camilla is. In fact, he's the only one who understands the psychological toll of Will's condition, identifying Camilla's well-meaning helicopter parenting as a contributor to Will's feelings of lost independence. That might not make up for his copious cheating and his abandonment of his parental responsibilities, but it shows that he's not the out-and-out bad guy he can seem like at times.