The second release of the band (and also in the year), Paranoid saw Black Sabbath lose more of their bluesy sound and instead, comes out heavier and darker. It is really evident that a lot of the material is anti war as reflected by the Vietnam war at the time.
This is THE album that gave birth to the Metal genre we have today if you still don't know. Whether you do or don't, it's time to relive some old classics!