My metal section consists of...
alternative metal, ambient metal, art metal, atmospheric black metal, atmospheric metal, avant-garde black metal, avant garde metal, avant-metal, black thrash metal, blues metal, british metal, brutal death metal, brutal metal, celtic metal, christian metal, classical metal, cold rolled steel metal, comedy metal, dark blue metal, death metal, doom metal, drone metal, experimental death metal, experimental metal, extreme death metal, extreme power metal, extremely powerful deathly metal, extremely dark blue metal, florida death metal, folk black metal, folk metal, funeral doom metal, funk metal, glam metal, gore metal, gothic doom metal, gothic metal, grind metal, groove metal, grunge metal, hair metal, hawaiian death metal, horror metal, industrial black metal, irish folk metal, japanese metal, jazz-metal, klezmer metal, latin jazz metal, math-metal, melodic black metal, melodic death metal, melodic heavy metal, melodic metal, melodic power metal, metal, metal metal, modal jazz metal, modern metal, neo-classical metal, neo-metal, new jack swing metal, new wave of british heavy metal, new wave of swedish heavy metal, nu-metal, old school death metal, old-school metal, operatic metal, pagan black metal, performance art metal, pop metal, post-synth revival atlantian extremely progressive black death metal, power metal, progressive black metal, progressive death metal, progressive metal, progressive sludge metal, progressive thrash metal, proto black metal, proto metal, psychedelic metal, punk metal, raga metal, really dark blue metal, rap-metal, raw black metal, soft metal, southern metal, speed metal, stoner metal, symphonic black metal, symphonic metal, tech death metal, tech-metal, technical death metal, technical metal, technical thrash metal, technical jazz thrash dark blue metal, third wave ska revival metal, thrash metal, viking metal, war metal, and white metal.
....just kidding.
I don't think you should really be that worried about what genre a certain band is "supposed" to fall under. When I rip an album, I give it a genre that I personally feel fits with the general sound. Sometimes, I even end up creating genres that probably don't exist outside of my computer.
However, if you're really adamant about following some strict guideline,
AMG has everything neatly categorized.