Immortal was one of the founding bands of the black metal style. Their early albums such as "Diabolical Fullmoon Misticism", "Pure Holocaust" and "Battles in the North" remain classics of the genre. The last two have hyper-fast tracks that nonetheless manage to express the grim atmospheres of black metal. Later they slowed down a bit and took a more melodic approach, the resultant albums are quite different and peraphs not in the spirit of the early black metal any longer. Yet they're enjoyiable, still very good albums.