The only player acquired in the Dan Haren trade that is likely to contribute at the major league level in 2010 is Joe Saunders, the 29 year old left-handed starting pitcher. This is Saunders' fifth season at the major league level, and he has compiled a gaudy 54-32 record with the Angels. While Diamondbacks' GM Jerry DiPoto compared Saunders' wins and winning percentage favorably to Roy Halladay, I don't think anyone really believes Saunders is close to Halladay's level as a pitcher. Let's start with a look at Saunders' traditional stats over his career.
2005 24 0 0 .000 7.71 1.500 2 9.1 10 8 3 4 4
2006 25 7 3 .700 4.71 1.415 13 70.2 71 37 6 29 51
2007 26 8 5 .615 4.44 1.519 18 107.1 129 53 11 34 69
2008 27 17 7 .708 3.41 1.212 31 198.0 187 75 21 53 103
2009 28 16 7 .696 4.60 1.430 31 186.0 202 95 29 64 101
2010 29 6 10 .375 4.62 1.492 20 120.2 135 62 14 45 64
Career 54 32 .628 4.29 1.392 115 692.0 734 330 84 229 392
Looking at these stats, we see that Saunders had his lowest ERA in 2008, and won 17 games that year, as well as 16 in 2009.  His ERA has been in the mid-4's in every season except for 2008 (ignoring the two games in 2005).  2008 was also the year with the lowest WHIP by far.  So what happened in 2008 to give Saunders such a good season, and how did Saunders happen to win so many games in 2009 despite a 4.62 ERA?  Let's look at some more advanced stats for Saunders:
Year ERA FIP xFIP K/9 BB/9 HR/9 BABIP LOB% Run Support W L
2006 4.71 4.08 4.33 6.50 3.69 0.76 .305 63.7% 5.84 7 3
2007 4.44 4.26 4.52 5.79 2.85 0.92 .336 72.7% 5.29 8 5
2008 3.41 4.36 4.65 4.68 2.41 0.95 .267 75.7% 4.52 17 7
2009 4.60 5.17 4.80 4.89 3.10 1.40 .290 73.5% 6.55 16 7
2010 4.62 4.70 4.94 4.77 3.36 1.04 .305 68.8% 3.94 6 10
Career 4.29 4.64 4.69 5.10 2.98 1.09 .294 71.8%
Looking at these stats, we see that Saunders' FIP (Fielding Independent ERA, which is based on strikeout, walk, and home run rates) has been pretty consistent over the years, although it has been increasing over his career. Looking at xFIP, which uses average home run rates rather than the actual rate, we see a similar increase throughout Saunders' career.  Both FIP and xFIP have been shown to be better predictors of future ERA than ERA itself.  What happened in 2008, when Saunders had his lowest ERA and WHIP? His BABIP (Batting Average on Balls in Play) was only .267, much lower than his usual career rate and much below the league average of around .305.  Also, his LOB% (Left on Base, or Strand Rate) was at a career high at 75.7%, so the runners on base were not coming around to score. Not surprisingly, Saunders was not able to duplicate these BABIP and LOB% rates, and he has never had an ERA or WHIP as low as 2008. On the surface, Saunders' 2009 season, where he went 16-7, looks like another good season. But his peripheral stats, especially his home run rate, were very poor that year. Therefore, his FIP and xFIP were also pretty bad. So how did he get such a good winning percentage in 2009? Run Support. That year, Saunders received an average of 6.55 runs from the Angels in the games he started. In fact, there were eight times that Saunders received over 9 runs of support - three times with 9, three times with 10, and two times with 11.  The high run support explains how Saunders won 16 games despite the high ERA. Saunders has actually been blessed with good run support throughout his career, except for the low 3.94 runs per game this season, which helps explain his 6-10 record despite the same ERA as 2009. Pitching Repertoire Saunders throws four primary pitches, two types of fastballs, a curve, and a changeup. Both his two-seam and four-seam fastball have a velocity around 90 mph. Saunders' change-up is around 82 mph, and he throws that around 20% of the time. He also has a slow curve that he throws in the mid-70s. Over his career, Saunders has been a little tougher against LHB than RHB - lefties have a .266/.324/.355 line against him, while righties have hit for more power at .278/.336/.450. He is a slight groundball pitcher, with a career GB/FB rate of around 1.27. Salary Saunders will have completed four years of service time after the 2010 season. He was arbitration-eligible during the last offseason, and the Angels offered $3.6M while Saunders asked for $3.85M. The two sides ended up agreeing on a salary of $3.7M before the arbitration hearing. Saunders can go to arbitration again after this year, and will be probably get a salary in the range of $5M in 2011.  How he performs during the next two months will determine if the Diamondbacks will bring him back next year, or if they will non-tender him during him the offseason. Obviously, the team hopes that he pitches well down the stretch, and that he becomes a solid #3 starter next year behind Ian Kennedy and Edwin Jackson. Summary So what should the Diamondbacks expect from Joe Saunders? His FIP and xFIP have been fairly steady in the mid-to-high 4's, with a slight upward trend. His strikeout rates have never been high, and have slipped below 5K/9 over the last few years, while his walk rates have climbed over 3BB/9. Even his home run rates have climbed over 1.0HR/9. Put it all together, and it probably adds up to an ERA in the high 4's. Maybe the switch to the NL will help a little, but pitching half his games in Chase Field will probably hurt. Saunders has been durable in his career, starting 31 games in both 2008 and 2009, and 20 games already in 2010. He typically goes up to 100-110 pitches per game, but he did throw 126 pitches in his last start with the Angels on July 23rd. He does have two complete games already this year, so he should help give the bullpen some much needed rest. He should get 11 starts the rest of the way - my guess is a 3-4 record, 4.77 ERA, 1.45 WHIP, 66 IP, 36K, 20BB, and 8 HR allowed.