Blood Fire Death is possibly the most essential metal album ever. After I listened to it, I began to understand black metal and death metal as genres, as expressions. It is the album that expresses Viking/Black metal at its purest, its most passionate, and most accessible. Now I understand what Immortal was trying to do, but they sound silly and contrived in comparison, to my ears.
I also fully came to appreciate Amon Amarth as more than a novelty. I saw the mantle of Viking Metal that they took on after Quorthon's death, and they wear it proudly. I've never had more fun at a concert than during Amon Amarth's set!