melocore

n. Broad genre of heavy metal and punk music that embraces hard, loud guitar riffs that nonetheless form a pleasing melody. Includes most power metal.

etym. Portmanteau of melody and hardcore, both referring to music

Some people get put off by Nightwish's heavy style as they do not appreciate the melocore nature of their songs. Linkin Park's song "Numb" also has the same issue.