What is the author's tone in Saint Joan by George Bernard Shaw?

In his Preface, Shaw suggests that his play is divided into three parts: "the romance of [Joan's] rise, the tragedy of her execution, and the comedy of the attempts of posterity to make amends for that execution." The first three scenes depict the rise, showing Joan's successes and "miracles" in a lively manner. In the next three scenes, the play becomes darker: Joan's enemies plot against her, her friends desert her, and she is put to death. The Epilogue for the most part restores the light tone of the early scenes as it depicts Joan's posthumous triumph, but it does end on a plaintive note, with another desertion of Joan.