Consider Dom Capers as the defensive coordinator for the Packers. He was inheriting a stout 4-3 defense that was good enough to help the Packers finish 13-3 and get to the NFC Championship Game in 2007. Capers is a 3-4 defensive coordinator, though, so a fundamental change in the offense was inevitable. During his first season (2008), the defense regressed dramatically, and was the primary reason the Packers fell to 6-10. But by his second season (2009), the defense rebounded after he was able to acquire more of the players he wanted and get rid of the guys who were incapable of playing in a 3-4 defense. The Packers had solidified the defense enough that they finished 11-5 and made the playoffs again. By the third season (2010), the defense was now entirely his, and it was one of the best, most opportunistic defenses in the NFL that season, and they won Super Bowl XLV. (The only reason it's regressed since is because they miss Nick Collins and need to find a new FS.)
This off-season is Todd Haley's time to mold the offense more to his liking. As we can see based on the amount of roster turnover on offense, there are many players who weren't good fits for his, and they're all gone now. Four of them were starters. Any time you have four starters who aren't a good fit for an offense (or a defense, for that matter), it's probably going to be inconsistent, just as the Steelers offense was last season. Let's see how it does now that Haley's taking a more active role in shaping it.