James often played his guitar with an open D-minor tuning (DADFAD), resulting in the “deep” sound of the 1931 recordings. James purportedly learned this tuning from his musical mentor, the unrecorded bluesman Henry Stuckey. Stuckey in turn was said to have acquired it from Bahamanian soldiers during the First World War, despite the fact that his service card shows he didn’t serve overseas. Robert Johnson also recorded in this tuning, his “Hell Hound On My Trail” being based on James’ “Devil Got My Woman.” James’ classically-informed, finger-picking style was fast and clean, using the entire register of the guitar with heavy, hypnotic bass lines. James’ style of playing had more in common with the Piedmont blues of the East Coast than with the Delta blues of his native Mississippi.
The Wikipedia entry, which is short of citations, paints a picture of a difficult person. Perhaps most intriguing is the tidbit that he “denounced” the version of I’m So Glad done by Cream. I couldn’t find elaboration on that, however.