This will not be a statistical comparison; rather a intuitive comparison of the two rosters. Looking at in 5 categories Offense, Bench, Defense, Starting Pitching, and Bullpen.
The 2009 lineup is missing Bay, Nady, and Bautista. It adds Moss, Morgan, and Andy LaRoche. On balance, the lineup lack the firepower of the 2008 lineup. If Moss develops, Andy LaRoche has a decent season, and McCutchen gets called up; we have a chance to score as many or more runs as last year. Freddie will hit better, Nate and Doumit will have decent (not great) year.
My reasoning is that while we scored runs before the Bay/Nady trades; we dropped off quite a bit after they left. This team might start out slow and get better as the season progresses. If (when) Adam LaRoche get traded, hopefully Hinske (with Pearce platooning) can replace LaRoche's bat.
I think this is a better bench than last year. More power, decent experience, better versatility. As long as none of the starters gets hurt, the bench won't have to play everyday.
It will be better than last year; especially when McCutchen arrives. Bautista , Bay, and Nady were below average. Andy LaRoche was below average last year; I think he will be better this year. Freddie will be better cause he is healthy. If Jack or Freddy go down, then Vazquez or Cruiz or Bixler would fill in. This could hurt our offense but may provide equal (or better) defense.
I think it is better than last year. While I don't think they will be great; I think they will out perform last years. Now this won't be hard to do.
While not having Marte will hurt some, I think this will be as good or better than last years.
In summary, this team won't play .500 ball or make the playoffs. But we will score as many runs as last year and give up less. Also, the team will be better at the end of the season than at the start.