What do you think about the melodic death metal genre?

I love melodic death metal; it has great music. But death metal just overwhelms the brain, and there's almost no music there. True, I haven't listened to much melodic death metal; I listen to gothic symphonic metal more. By the way, what's the difference between metalcore and melodic death metal? I like Children of Bodom, Dark Lunacy, Diablo; I don't think I've listened to anything else in detail.