I am aware that most would not consider Uriah Heep a metal band, but I thoroughly enjoy their music, and their indispensable influence on heavy metal is what made me initially stsrt listening to them.
To start off, this record was released in 1970, and it is heavy as all hell, especially considering the time, but, beyond that, its progressive song structures, fastidiously written solos, and overall powerful sound were very key to the later sounds of heavy metal bands, specifically iron maiden (which would go on to influence many other bands, of course).
Songs like "High Priestess", "Time to Live", and "Salisbury" are great examples of Uriah Heep's creativity and obvious influence on many rock and metal groups. So if you'd like to hear a band that was very revolutionary and innovative during their time, check out this album, as well as Uriah Heep's other classic records, like "The Magician's Birthday" and "Demons and Wizards".