The success of the bullpen hinges on several factors.
First of all, Kerry Wood has to stay off of the DL—something he hasn't been able to do for the majority of his career. When he's healthy, he gives the Cubs a very valuable arm coming out of the bullpen. According to Bruce Levine on ESPN.com, Wood will assume the setup role to start the 2012 campaign. However, due to to Wood's almost magnetic attraction to the disabled list, the Cubs will likely limit him to around 50 innings this season.
Second of all, the lefties—John Gaub and James Russell—have to be effective when called upon. The Cubs are lucky to have two southpaws coming out of the pen, but that advantage means nil if Gaub and Russell fail to get hitters out with any sort of consistency. Gaub, who came to Chicago in the DeRosa deal with Cleveland, has minimal major league experience (2.2 innings last year), but loads of potential. During his time with the Minnesota Gophers, his fastball was apparently consistently clocked in the upper nineties. A shoulder injury during his sophomore year knocked a few MPH off of his heater, but hits the mid-90s on the gun with regularity.
Russell has been decent at best for the Cubs over the last two seasons. However, there is reason to feel optimistic about the young lefty in 2012; he improved in four major statistical categories last season, including ERA, WHIP, HR/9, and BB/9. And, at age 26, he still has time to improve his game and find his niche in the Cubs bullpen—whether that be as a setup man or a middle reliever.
Most importantly, however, Carlos Marmol has to rebound from an absolutely horrendous end to the 2011 campaign. He posted a National League worst 10 blown saves and looked nothing like the confident, nearly untouchable flame thrower that Cubs fans had come to trust during the 2009 and 2010 seasons.
But still, there is hope for Mr. Marmol. Before last season's meltdown, he was one of the most reliable relief men in the game. In 2010 he tallied 38 saves and a 2.55 ERA. He's not as young as some may think (29), but he still has time to turn his game around.
With Hoyer, Epstein, and Sveum revamping the lackadaisical culture that has surrounded Cubbie Land for the past few seasons, Marmol may very well return to his old, respectable form.