So many forms of metal, bands even got to the point they make up there own style of metal just to sound unique, You got metal, Death metal, Soft metal, black metal, heavy metal, Christan metal (wtf?), doom metal, gothic metal, copper metal, steel metal, zinc, gold, silver, ect....
Seriously it all sounds like fast ass guitar and words you can't understand without reading the lyrics anyways
And as for melodic death metal: Carcass - Heartwork
This CD was a huge influence on the development of melodic death metal. Gothenburg bands added more melodic riffs and such making melodic death metal what it is today