Metal roofs are fairly popular out here, they don't catch on fire. Discount on homeowners insurance.
They 'sweat', need a real waterproof underlayment (15-30lb felt just don't cut it)
They sound neat when it rains. Real neat in a hail storm. Snow can be a minor(?) issue, especially when it cuts loose all at once
Roof penetrations (any penetration) can be leak points, and often are. Same for valleys. Composition shingles 'flex', the whole panel(s) move on metal.
Durability is generally longer than composition shingles, I wouldn't call them life time though.
They dent (big hail, big branches, 400 lb gorilla), they're real slippery when wet, the color fades over time. Roof repairs end up looking like a checkerboard.
Rick