They were terrible songwriters and clubfooted musicians who possessed an amazing riffmeister, so that their classic songs start out with an awesome, godlike riff that melts into your brain, and then proceed to pummel your brain over and over and over and over with that riff for the entire song. The song itself has little else going for it BUT the riff. This weakness is especially glaring on the debut. And Master of Reality, but I like that third one better.