There's not a lot to say about Mark Ellis beyond the likely and disappointing possibility that his average 2011 with the Rockies may still represent significantly better production than any second baseman we use in 2012.
After the Rockies decided to give up on Jose Lopez , the Rockies needed somebody new to stabilize the second base position, which as usual was the team's biggest void as it generally has been throughout its post-Eric Young history. The answer, in this case, was not Jonathan Herrera, but instead the newly acquired longtime-Athletic Mark Ellis. Ellis had been struggling mightily for the A's after they picked up the 2011 option on his contract. Available for a moderately cheap price (Bruce Billings and eventually Eliezer Mesa as a player to be named later), Ellis' career stability, defensive skill and relative ease of acquisition was enough to pull the trigger at the midpoint of the season.
Ellis did indeed improve significantly from an offensive standpoint after the trade, demonstrating better production in nearly every area. While he was not the most appealing option going forward due to his age, it became clear early on that he may be a viable option moving forward beyond the 2011 season thanks to his generally consistent performance. Generally filling the two hole in the lineup (but occasionally jumping about), Ellis ended the season as easily the Rockies' greatest second baseman of the season. After being a replacement level player with Oakland for half of the season, Ellis battled back into the positive contribution in his time with the Rockies, thanks in part to his solid defense.
As Ellis declared free agency with the start of the offseason, he was identified as a likely candidate to return to the Rockies, provided they freed up some salary. Unfortunately for the Rockies, before they began their roster rearrangement, the second base market had heated up with the quick signing of Aaron Hill and Jamey Carroll. One by one, the free agent middle infielders began to sign, with the Dodgers scooping up several, including Ellis. He is expected to be their starting second baseman in 2012, and the sudden disappearance left the Rockies with yet another void up the middle across the bag from Troy Tulowitzki, and it still hasn't been filled as of this point.
My grade for Ellis' season is B- provided it is based only on his time with the Rockies. During the period of July-September, Ellis was comparatively average to most MLB second basemen, with his value contributing specifically to the important plugging of a lineup hole. While he was not the kind of player that could have elevated the team to contention in the second half, he did not demonstrate himself to be any real part of the problem either. Ultimately, what we saw was a league average second base performance that helped some but not a lot, and which may yet still be superior to any second base action we see in 2012 barring as of yet unforeseen circumstances.