In most sports, a player that does well their rookie season is often victim of the Sophmore Slump in his second year. Andy Dalton did a great job in his rookie season. He led the Bengals to a 9-7 record and a playoff berth as well as earning a spot in the Pro Bowl. That is very successful for a rookie QB, especially one that plays in the AFC North, arguably the toughest division in the NFL.
After such a solid rookie season, it is going to be tough for Dalton to replicate his success. Teams know more about him and they have more film to watch to be able to better prepare against him. This will hold especially true against the division rivals. They play against him twice a year. They see him more and know him better than anyone else. The other 3 teams in the division all have solid defenses. The Steelers (1st), Ravens (3rd), and Browns (10th) all ranked in the top 10 in overall defense a year ago.