The Bulls were the most hard-working, dedicted team in the league, and it paid off in them posessing its best defense. The Bulls owned two elite-level defenders in Joakim Noah and Luol Deng, impressive depth (especially in the front court), and a naturally coachable roster overall, but it was the arrival of rookie head coach Tom Thibodeau that set the tone early and often that defense was going to be the key in Chicago. Coach Thibs employed an active and swarming scheme that forced opponents into a struggle for not only every game, but every single posession.
But beyond reigning MVP Derrick Rose, the Bulls were merely an average offensive team. Credit goes to Thibodeau for encouraging his players to be more of 3-point threats, but while Rose and Deng showed improvement (especially when it came to volume), there is still not enough shooting outside of Kyle Korver to adequately punish defenses for collapsing on Rose. Another flaw with the team's offense was the lack of other playmakers on the floor. With Derrick always serving as the intial option, there was rarely much else seen when that was taken away. Some of that was a lack of originality in the offensive scheme, and Thibodeau still has room to improve as a coach on that side of the court. But there was also nobody else on the floor who could improvise their way out of a bad posession.
The Bulls played to their strengths last year and it worked for them very well. But to get to the Finals and get their first non-Jordan title, Rose is going to need some more help on offense.