Complex sentence: After Oyamada went solo, he became one of the biggest Shibuya-kei successes, with his 1997 album "Fantasma" considered one of the greatest achievements of the genre.
Split into simpler sentences: After Oyamada went solo, he became one of the biggest Shibuya-kei successes. His 1997 album "Fantasma" is also considered one of the greatest achievements of the genre.