+ I agree with Bleacher Report's assessment that Chad Johnson's struggles is related to the difference in the team's quarterback. With Carson Palmer between 2004-2007, Johnson averaged 93 receptions, 1,378.8 yards receiving and 8.3 touchdowns. Against those averages, with Palmer playing some in 2008, Johnson missed his averages by 30 receptions, 838 yards receiving and four touchdowns.
However, I also don't think it was that simple; there's other things to take into account.
Even though Ryan Fitzpatrick isn't Carson Palmer, the Bengals offense struggled early. Johnson and T.J. Houshmandzadeh stayed away from Cincinnati during voluntary workouts where quarterback and receiver can establish their timing and get comfortable with each other. Even Houshmandzadeh struggled with six receptions and 70 yards receiving through the first two regular season games. Johnson slowly returned to camp after rehabilitating a procedure on his ankle in which delayed his participation during Training Camp. Then he tore up his shoulder during pre-season against Green Bay. Plus, he didn't want to be a Bengals receiver anymore; so it's feasible to assume that his effort just wasn't there like before.
You have to also consider the Bengals offensive line struggles. Even though Bengals quarterbacks were sacked 51 times, they were constantly pressured to throw before the developed route, causing inaccurate passes hoping to avoid the sack. In fact, having Fitzpatrick benefited us at times with his crazy legs sustaining drives.
Then there's the rushing offense early in the season. Terrible. Just terrible. When you keep the secondary back because there's no threat of a rushing offense, it tends to challenge the entire passing game.
By the time the Bengals established some momentum in the second half of the season, Johnson went inactive due to injury. All I'm pointing out is that Johnson's 2008 struggles was far from a simple quarterback change. No matter how you spin it, nothing came together in 2008.