Went and saw it again this past Saturday. Wasn't blindsided by the emotional sucker-punches this time around, but that first scene still got to me. I wouldn't go so far as to speculate whether James Gunn is a believer or not, but there are Christian themes woven throughout, including no less than three pictures of sacrificial love and the impact of grace in a person's life, as exemplified in Star Lord's decision to make a difference for the good after circumstances free him and his friends from prison.
Probably won't get another chance to see it again until the Phase II boxed set arrives.