The main knock on Santo's Hall of Fame case is the length of his career...he debuted at age 20, but his last good year was at age 33, and after a bad age 34 season with the ChiSox, he retired.
B-R has Santo with the 7th highest WAR of any third baseman since 1901, trailing only Mike Schmidt, Eddie Mathews, Wade Boggs, George Brett, Chipper Jones, and Brooks Robinson.*
* Santo will be passed in career WAR this year by Scott Rolen, who I suspect will also be shafted by the Hall of Fame after he retires.
There are only 10 major league third basemen in the Hall of Fame, which is a separate issue, of course...but Santo is clearly worthy, and it is a shame he passed away before the Veteran's Committee could rectify its mistake.