After spending much of my life believing Black Sabbath to be wholly evil (as a child in the Evangelical Church) or wholly outdated (as a self-serious hipster), I’ve spent the last couple years slowly working my way through their catalogue—and learning just how wrong I was.

Throughout the early records, the band gets progressively heavier with each release. Sabbath Bloody Sabbath certainly doesn’t stop that trajectory at all, but neither does it rely on heaviness alone as a compositional device. The result is some of the most cathartic and gorgeous music ever written.

I’ve owned Paranoid for over a decade now, but for whatever reason, I believed it was merely of historical import—a curiosity piece from the early days of heavy metal. And through a precursory listen, there’s not much on that album to challenge that opinion.

But after adding Master of Reality and Vol. 4 to my collection, I’ve become fully convinced of both their historical significance and their timeless appeal, which is what bade me purchase this album without hearing it when I found it at my favorite used shop—a gamble that has certainly paid off.

As I progressed through their career, the songs get noticeably lower and louder. Many of the songs on Paranoid sounded like the blues played with a lot of distortion, while the later albums had tracks that sounded pretty close to modern doom metal. Tony Iommi dropped from drop D to Drop C# tuning, the amps got louder, tempos got slower, and Ozzy’s voice got even higher.

In the early moments of the self-titled track, it feels like that trend is continuing. Tony Iommi offers up his sludgiest riff yet—so low and slow that for a moment I had to check if I was playing it at the wrong speed before the rest of the band entered. But during the chorus, something unexpected happens: acoustic guitars. It’s an almost whiplash-inducing turn, but it feels more relieving than jarring—a testament to their mastery as composers.

The rest of the record is filled with similarly satisfying experimental turns, such as the Moog synthesizers that augment the atmosphere of “Sabbra Cadabra” (hey, that’s Yes’s Rick Wakeman!) or drive the instrumentation of “Who Are You?” “Looking For Today” has another acoustic interlude—this time aided by a flute (also played by Iommi). Closer “Spiral Architect” is an epic work of studio trickery, implementing layers of electric and acoustic guitars, a string section, Bill Ward on timpani, Geezer Butler’s nose flute, and even Iommi on bagpipes. It crosses firmly into Who-esque rock opera territory while still unmistakably Black Sabbath. Had my opinion of the band not shifted in the last year or so, it would have come as a major shock.

“Still unmistakably Black Sabbath” would actually work pretty well as a four word description of the album, because for all of the expansion to their sonic palette, there is no mistaking this album for anyone else. And there’s still plenty of signature weapons in their arsenal. The six minute “A National Acrobat” marches with a wah-pedaled chuggy riff with Butler and Ward holding down the groove, until the whole mood shifts five minutes in. “Killing Yourself to Live” rides an effect-heavy groove reminiscent of “Paranoid” as Ozzy wails Butler’s moralistic lyrics about the dangers of the rock star lifestyle, jumping between tempos as the track progresses. And throughout the album, Tony offers a number of guitar solos dubbed on top of one another to deliver the band’s signature chaos.

In the words of Ozzy himself, Sabbath Bloody Sabbath was “Our last truly great album, I think… And with the music, we’d managed to strike just the right balance between our old heaviness and our new, ‘experimental’ side.” And given the mixed reviews for the few albums that would follow, he might be right. But regardless of the context within their larger catalogue, Sabbath Bloody Sabbath is an absolute masterpiece.