Along with The Tumbler and the subsequent Road to Ruin, Stormbringer seems to have been consistently under-rated -- as the above reviews confirm. There is a timeless charm and, and an even rarer [especially nowadays] quality, A SENSE OF FUN AND ADVENTURE running through these recordings that makes quibbles about how good a songwriter or singer Beverley is/was verging on the redundant. However, if an answer is required, Beverly's brooding contralto sounds pretty effective here and her songs [esp I Can't Get the One I Want] stand up well alongside's JM's admittedly cooler efforts. [Incidentally Francoise Hardy, a good judge of a song, covers two of Beverly's Stormbringer songs, on her excellent If You Listen album, which is also well-worth checking out].
In short, Stormbringer is a superb example of early 70s folk-rock, an album that effortlessly smites most modern folk-rock acts out of the park.
Just listen, without prejudice, and let the thing wash over you.