Okay, now for maybe a weird but not necessarily controversial statement.
I've realized I have for a long time been subconsciously categorizing metal into two groups in my mind, transcending whatever actual genre they are in. I can't put an exact label on them, but the closest I can describe it as "rural" vs "urban" - At any given time I really only want to listen to one or the other. I can't even really qualify what makes me put what where. I suppose the "rural" styling maybe has more flowing and organic song structures. Maybe even less abrasive vocal styles? There's definitely a lot more to it but I can't exactly find a good way to describe it...