Vol. 4 has all the messiness of a heavy metal Exile on Main St., and if it lacks that album's overall diversity, it does find Black Sabbath at their most musically varied, pushing to experiment amidst the drug-addled murk.
Ozzy Osbourne's wail is becoming more powerful here, taking greater independence from Tony Iommi's guitar riffs, yet his vocals are processed into a nearly textural element on much of side two.
Parts of Vol. 4 are as ultra-heavy as Master of Reality, yet the band also takes its most blatant shots at accessibility to date - and then undercuts that very intent. The effectively concise "Tomorrow's Dream" has a chorus that could almost be called radio-ready, were it not for the fact that it only appears once in the entire song. "St. Vitus Dance" is surprisingly upbeat, yet the distant-sounding vocals don't really register.
The notorious piano-and-Mellotron ballad "Changes" ultimately fails not because of its change-of-pace mood, but more for a raft of the most horrendously clichéd rhymes this side of "moon-June." Even the crushing "Supernaut" sticks a funky, almost danceable acoustic breakdown smack in the middle.