WAR is a cumulative stat. You cannot use this season to come up with an average WAR. He also was hurt in 2012 and didn't play full time in 2009, further worsening your average WAR stat. When you take that into consideration, 3.1 is pretty freaking awesome. In fact, remove this year (since it's only 1 month in it would be the wise thing to do) and his average WAR minus 2011 is 3.83. If he played full seasons in 2009 and 2012 it would be easily over 4, which is considered All Star level.