Complex sentence: Their style was more traditional in the beginning of the 1980s, shown on the "Burning the Witches" album, but soon going more to a hard rock and glam metal style starting with "Hellbound".
Split into simpler sentences: Their style was more traditional in the beginning of the 1980s, as heard on the "Burning the Witches" album. They soon moved to a hard rock and glam metal style, starting with "Hellbound".