I pretty much bought this album because of a personal doom metal resurgence of sorts. I'm still not an Ozzy fan, I bought this for the music. Master of Reality is perhaps one of the pioneers of doom but music journalists deem it as stoner / sludge rock. Until a definitive music theory separates these genre comprehensively, I am happy to treat is as doom. The tempo & arrangement pretty much defines doom as we know it today. Mind you, doom itself was a term coined retrospectively; someone said it's doom then did a throwback trawl & realized Black Sabbath sounded like they pretty much started the movement.
In any case, I'm embracing how down-tempo plays a very big part in doom. In my metal domain, speed is essential so when speed plays a lesser part in this sub-genre, it doesn't sit well with me. Then again, doom has a heavy emphasis, not speed. Iommi's work here pivots on his magnificent riffing more than his solos; they sounded very bluesy but that's what you get if your ideas are rooted in the pentatonic scheme of things. Master of Reality is enjoyable. It could have been a blast if the fuzz was properly generated but hey, it's done in 1971.