Metallica and melodies

I haven't listened to Metallica for a long time. A few days ago, my love of Metallica got very much, and i wanted to listen to them. I asked to one of my friends and he gave me a cd. Today i was listening of Metallica and In Flames all day. But i understand that, i like hard musics of Metallica more then softs. By the way, i understand that melodical songs are better then others. And also melody must make me happy, otherwise i find myself as a psycopath.