Hey, Im also a metal head. Ive been in a couple of metal bands playin drums. What i notice when our singer used to write lyrics is that.....they really werent too much different from anything else you would hear. Its all about grooving the melody into the music. I suggest that you read a couple of poems and get some insight. Its a good way to start from scratch. Dont worry about "being hardcore" I listen to alot of metal i.e. It dies today, parkway drive, as blood runs black, war of ages.... when you actually read their lyrics you could almost imagine them being lyrics in any other type of music. Kinda like killswitch engage with holy diver. The band makes it metal...not the lyrics.