There should be more poll options. They were one of the first bands using that early metal sound, what with Page's distorted riffing and the incorporation of blues into a rock setting; this was also popularized by Sabbath, who marked the point at which metal really began to take off. They were predominantly a metal band, but not in the modern sense, although one could surely argue hard rock. Fuck it, I guess I'll just say that rather than being a metal band, they (along with several other bands) formed the basis for metal, which many bands would adopt in the future.