From where I'm sitting, there seems to have been something of a consensus shift regarding the collected works of post-Ozzy Black Sabbath. The opinion that the band's first four albums – all fairly inarguably brilliant as they are – is all you need from their canon has been widespread enough to act as received wisdom. Maybe this was something to do with the popularity of stoner rock as a genre, a decade or so ago, but the upshot is that, in this mode of thinking, the Birmingham-birthed titans' early 80s reinvention gets summarily dismissed as histrionic rock radio-ready Dungeons & Dragons cheeseballery with a comedy shortarse singer who collects porcelain frogs. Ronnie James Dio-era Sabbath is a betrayal of the true grail.

Now, this notion is pretty much horseshit, or at least a needless oversimplification. So it's pleasing that in the last few years, albums like these two (which are both getting reissued by Sanctuary in tasty double-CD packages, as part of their ongoing Sabs re-up programme) have been given more chance, in the world of the opinionated blowhard, to be assessed on their own terms. Whether it's down to the band touring regularly, a general resurgence of appreciation for purist, escapist heavy metal, or some combination of these factors, may these records continue to get their dues as countless downtuning hairfarmers have paid theirs. Neither Heaven And Hell nor 1981's Mob Rules are perfect records, but Black Sabbath never made a perfect record; it's arguable that in many ways, their flaws went a long way to cementing their greatness and mythological status.

Heaven And Hell finds bassist Geezer Butler stepping back from his role as primary Sabbath lyricist; Dio had made his fixation on fantasy-scene derring-do apparent to 70s rock consumers with his work in Rainbow, and had indeed left that band as a result of this element being diminished. He reins it in a tad on this new venture, but the contrast to Butler's musings is pretty clear. At the risk of simplifying somewhat, Dio writes about fantastical subjects with a layperson's simplicity; Butler brings high drama to issues rooted in reality. Either way, it's fair to say that the singers are more important in these instances than what they're singing. 'Neon Knights', the opening track and lead single, comes off as a statement of intent: it runs at a pace unusual for these figureheads of lumber, with a Tony Iommi solo that's notably more fleet-fingered and flashy than his average, and could almost be described as 'pop-metal' while still managing to sound like Sabbath. It didn't do badly in the charts, either.

Long-term Sabs headbangers were no doubt sated by what followed on the first side of this eight-song album, though. 'Children Of The Sea' and 'Lady Evil' – how intentional is it that these songs are titled so similarly to old numbers by the band, one wonders? – both grow from inauspicious beginnings (Zep-ish acoustic guitar in the case of the former) to doomy mini-corkers which would have done the band proud at any point in their existence. The title track – the disc's longest at seven minutes – starts at a sinisterly sombre pace, drifts off halfway through into a wasteland of soloing of the type employed during gigs to give the knackered drummer a quick break, and speeds up to a meaty canter as Dio underlines his thoughts on moral dualism. Plus I spent about five hours the other day trying to extract its main riff from my head.

Side two (he wrote, as if at ground zero for the release of a record that actually came out two months before he was born) doesn't quite hit the same heights. 'Wishing Well' paddles in the same semi-pop waters as 'Neon Knights' without being nearly as memorable; 'Walk Away' gets a pass thanks to another terrific riff and perky drum fills, although its overall construction isn't made of full-beam greatness. We finish with 'Lonely Is The Word', which uses the words "the back side of the moon" in its first verse (surely any listener in 1980 would have assumed this was a Floyd reference, and found it pretty peculiar?) and is defined by a guitar solo that's like a decade's worth of Jimmy Page being appropriated by AOR, condensed into three minutes. Still a decent song, but not what many came to Sabbath records for, I daresay.

Mob Rules was released 18 months after its predecessor, and while this reflected the freshened work ethic of a band that had spent most of the late 70s obliterated into inactivity, it was far from a trouble-free time for the band. Drummer Bill Ward was fired in the middle of a tour as his drinking problem worsened, and his eventual replacement, Vinny Appice, helped to usher in a further tweaking of Black Sabbath's signature sound, his pounding being more conventionally hard rock than Ward.

One thing which remains through the transition is the approach to album structure, the opener once again being a catchy, quick banger with solos peeled off everywhere. 'Turn Up The Night' in fact suggests the band learned a few tricks from one of the most successful bands to follow in their wake, Judas Priest. Likewise, 'The Sign Of The Southern Cross' revisits 'Children Of The Sea''s manoeuvres by drawing you in with some fey acousticisms, giving the snail-slow riff an extra kick when it presently arrives. It's a couple of minutes too long, though. The pretty-much-ballad 'Falling Off The Edge Of The World' is this album's 'Lonely Is The Word', and pretty naff with it.

It wouldn't be wholly unreasonable to look at Mob Rules as a consolidation of the territory Sabbath clawed back with Heaven And Hell, which was a critical and commercial rebirth of a band widely considered to be dead in the water. The quartet had located a formula, or perhaps a number of mini-formulas, and could be forgiven for wishing to milk them while the going was good. (It wasn't to be, as Dio left the band in late 1982, sending the band into a purgatory of inappropriate vocalists on flimsy LPs, but that is another story.) They certainly switch up styles with a sort of flair: 'E5150', a bizarro instrumental piece that would probably get called 'hypnagogic pop' if it was released now, on cassette, in an edition of 100, leads into the triumphalist title track which leads into 'Country Girl', one of the most unabashed good-timers in the band's canon (its lamentation for a lost love notwithstanding).

In terms of the extra gubbins that justifies calling these two reissues 'packages', neither album's second disc sheds any particularly fresh light on Dio-era Sabbath, oft-misunderstood beast that it is. Heaven And Hell mainly collects live tracks from 1980; Mob Rules edits three London shows over the 1981/2 NYE period down to a single CD. Dio's pipes are about as in-form as could be hoped for; the band maintain the ability to turn rigidity into pliability via jamming, and perhaps telepathy. Additionally, many of the archive photos are worthy of unearthing solely for the childish amusement factor of noting the different ways in which the snapper has tried to disguise Dio's limited stature.