I should declare an infatuation – this album is exactly as old as me and for 25 of its 40 years I have loved it unreservedly. This can't be a review of the album because if you need to be told whether The Slider is any good or not you've clearly never had your Marc Bolan moment - the moment when your soul just opens up another antechamber where only his warmth and powers can reside, just here next to your heart tucked in with a grin.

It's surprising how many people haven't shared this moment. It's surprising how so many are still in hock to the press' worst habits about Marc Bolan, seeing him as punchline or pale imitator of more dependable innovators like Bowie. My first TRUE Marc moment, even if the initial devastations of '20th Century Boy' and 'Solid Gold Easy Action' (from that classic mid 80s white-sleeved Best Of) hadn't already wrought their wreckage across any possibility of calm or level-headedness about this man, was from an album my sister's friend had nicked from HMV in his big self-designed robbing pocket.

It was a record called Electric Warrior and it was the first, second and last tracks that held me to a flame: the stealth and shimmy of 'Mambo Sun', the way 'Cosmic Dancer' physically turns your heart inside out, the way 'Rip Off' had a coda that was just something I'd never heard ANY band do before, this gorgeous hung caesura of drone strings and raga-sax and the cubist-boogie bedlam that it evanesces out from – THAT was my first Marc moment, the moment I twigged this wasn't about 'wizardry' or 'elfin' magic, it was about real, disciplined, collaborative magic and Marc simply wrote songs like no one else.

It's a Marc moment when you realise you're not gonna have to just admire his craft, but let in and love his style, which infected everything from the top of his locks to the soles of his brothel creepers to the curious, wonky way he wrote, to the brilliantly simple, massively educational and inspiring way he played guitar. Knowing the president's weird he's got a burgundy beard, seeing the girl dance with the manskin pants at the governor's ball, Marc marshals your vision in sound and word, pulls you close to his own strut, the cut of his own post-mod, unconvinced, last-gasp, knowingly futile and therefore committedly absolute moves of resurrection for rock & roll.

The Slider I came to later, and initially found it too eggy. Too rich. Too much sugar. I missed the bonehead repetition and finely-finessed heaviosity of 'Mambo Sun' and 'Planet Queen', found too many songs seemingly attempting to replicate equivalents on Warrior. I considered 'Mystic Lady' merely an attempt to recapture the wonder of 'Cosmic Dancer'; 'Main Man' toying so closely with the same melodies as 'Life's A Gas'. But there were a couple of tracks that, with total immediacy, robbed me of any faculty other than slack-jawed drooling: the angular ferocity, nuclear thunk and amp-stack avalanche of 'Buick McKane' and the truly demented time-sig fuckery of 'Chariot Choogle'. To get to them you had to hear most of both sides, so slowly everything else on the record came to eclipse anything that had come before.

For I realised that my fatal mistake was to see The Slider in relation to Electric Warrior. One is an announcement. The other is perfection of that initial statement, and a deeper wider exploration of its creator as a result, something in which everyone, not just Marc, steps (and tightens) up their game, hones the perfect surface to contain the increasingly heated and confused interior, keep the dream impossibly even more rock-solidly intact than it had been before. That's the odd journey tripped by The Slider, in contrast to rock & roll's usual habits of wastage and loosening. It's an album of progression that actually makes for shorter songs, writing drawn-taut to impact, with absolutely every last trace of bearded meandering razor-cut and jettisoned. This is Marc's first full-tilt attempt to sustain a pure pop impetus over the course of a whole album and there can be no question, as 'Metal Guru' careens itself into your day like the great big walloping slab of wonder it eternally is, that he's gonna go harder, faster, deeper than he ever has before.

"I like my songs to be durable to the ear and exciting to the mind. My lyrics always come before the music. Repetition comes into my songs a lot because I think my lyrics are so obscure that they need to be hammered home. You need to hear them eight or nine times before they start to make sense. I don't see anything wrong with that" – Marc Bolan, interview, 1972.

'Metal Guru', here given an extra physicality and space by Visconti's amazing remastering job (throughout, this is like returning to an old friend who's improbably got better looking in the intervening two-score years) is a song of self-regard, a dawning awareness that the stars and starlets Marc always sang about might now be gathering around his own flame, the question 'is it you' (alongside 'oh yeah', the line you sing the hardest) surely addressed to himself, surely sounding himself out about his readiness for superstardom. Almost to balance out this narcissism, the sumptuous 'Mystic Lady' would seem to be addressed outwards – in fact it's clearly again sung to the mirror, "the people in your life are cruel / keep on riding that hard road / the lovers in your life are few/keep on riding that hard road". This is not the man who made Warrior, this is a man who's learning how to hide, who's had to learn how to live with hatred (the snobbery/snideness of Marc's critics early on is still startling), who's trying to find his own private plateau where his visions can be enacted. The hippy/free-festival scene which had birthed him had revealed its own reactionary snobbery since he'd pulled the Judas Dylan move of going electric – he was now, truly, out on his own.

"Hippies aren't consumers and the records we made didn't sell very well. I wasn't really aware of the charts but I knew that I was getting bored with the music. I was bored with not being recognised. I wanted to make an impact because there mightn't even be a world left in ten years. So I went electric for 'Ride a White Swan' and put on a string quartet. The record company didn't think that it would sell at all but I was sure it would. It did after being played to death at the Isle of Wight festival. John Peel thought we'd sold out and I can see now that he was helping himself more than us. He needed an obscure group he could use and we were that group. He didn't like 'Ride a White Swan' at all. I think he was paranoid that we would do anything that was even remotely commercial. I haven't seen him since and he certainly never plays our records now" – Marc Bolan, interview, 1976.

'Rock On', 'The Slider' and 'Baby Boomerang', like the divinely lopsided 'Baby Strange' on the flip, lay bare Marc's method, or rather the way he couldn't help but derail the straight ahead and methodical with his own curious mix of abilities. While I normally abhor the glut that box-sets provide, the demo versions (on disc two) of these songs do actually reveal exactly the roots and tangles Bolan went through to create them. On the one hand each is a conventional rock song, based on the kind of keynote musicians (Leadbelly, Robert Johnson) he always carried with him, the old songs he always loved. In 1972, when asked what singers he liked, he was proudly out of touch with the white mainstream who loathed him so much: "I like a lot of old blues singers, you know Bessie Smith is an old blues singer I liked a lot, you know. I can't really think of anyone, Robert Johnson maybe, someone like that, but I can't… no contemporary singers. When I'm in America I tend to listen to more black stations".

Unlike virtually all the other blues-copyists and Eric C*ton-style authenticity-merchants then rehashing vintage motifs however, Bolan knew to keep the vital element of surprise, freakishness, ODDITY alive in his re-imaginings of those classic patterns. Anyone hearing 'King Of The Delta Blues Singers' or the 'Rockin Chair' album knows how fucking WEIRD those old guys'n'gals were, how they managed to always so massively problematise the supposed musical dead end they were operating in, blow those 12 bars to infinity. So 'Rock On' is peppered with strange crooks and bends, queer turnarounds and maverick twists that genuinely put it, in a song writing sense, closer to the blessed singularity of your John Lee Hookers & Howlin' Wolfs than anyone who could play at a billion miles an hour could even dream of. In fact, in an era of plank-wankers intent on turning the blues into a virtuosity contest, Bolan's insistence on peopling those old types of music with his own cast of characters and his own heteroclite musical imagination created an entirely new sound. Playing to to his limitations as a guitar player, 'The Slider''s nagging treble jabs and 'Baby Boomerang''s loose-limbed boogie-funk emerge as a whole new peculiar form, Visconti zeroing in on Bolan's unique idiosyncrasies and applying them to the entire arrangement.

'Spaceball Ricochet' is perhaps the most personal, moving song on The Slider, summing up Marc's inherent compassion, yet also his increasingly precarious sense of disconnection with his own phenomenon. "With my Les Paul / I know I'm small but I enjoy living anyway / book after book I get hooked / every time the writer talks to me like a friend / Deep in my heart there's a house that can hold almost all of you" – it sounds, amidst the clamour around it, like a quiet, hopeful statement of a gentle intent, a tiny moment of levitational poise within which he regains his breath, focuses his spirit. After that brief respite, the overload continues on 'Buick McKane', clearly possessed of the same unhinged hunger as 'Rip Off', a riff that moves with the beautiful imbalance and unselfconsciousness of an animal, teeth bared, body heaving, waiting to pounce. 'Telegram Sam', that kicks off side two like it's wearing seven-light-year boots, might've become so ingrained in your mind that you've stopped actually listening to it, but here again the remastering reanimates the recognisable. The tactile and tremendous re-rub that Visconti has brought to bear on the whole album really pulls things to the surface like never before, the rhythm section locked together in supremely relaxed, maximally impacted putsch. Perhaps the best song about an accountant to ever get to number one, 'Telegram Sam' really emphasises the collaborative nature of what makes so much of The Slider work - when Bolan growls "Me I funk" it's believable because he's backed by Bill Legend, Mickey Finn and Steve Currie, one of the best and most underrated rhythm sections in pop history.

The backing vocals by maverick genii ex-Turtles Flo and Eddie seal it all to your heart - everyone, including Bolan, was willing to step out of the spotlight when necessary, pop perfection the clear ideal. 'Rabbit Fighter', like EW's 'Lean Woman Blues' initially daunted me with its explicit blooze-classicism but unlike 'Lean Woman' it transforms its sources again through the eccentricity Bolan brings – the strung-out orchestration, the sheer ugliness of the solos, the killer homage to another of Marc's unlikely heroes – "Moondog's just a hero to the end".

'Chariot Choogle' still totally pillages my dome – quite why they thought it'd be a good track to sell the T.Rex idea to Americans is beyond me, so asymmetric is its lunge, its Barrett-like cock-eyedness far too psyche for the times it came to save, the lyrics another she/he/her/me four-way dialogue between Bolan's self-image, real persona, public face and private conviction. You know who you are. Gonna walk upon the waters go ooh ooh yeah. The promo film for The Slider that features 'Chariot' and 'Buick' is part of the extras here, which also include a gorgeous sheet-music book, badges, fan-club letters, a sew-on patch (!), concert tickets, an extra disc of demos and out-takes, and a DVD with a long exhaustive interview with Visconti as well as TV footage from TOTP and ITV, all from roundabout the time The Slider came out. Where ordinarily I find reissues full of too many pointless distractions, a dispelling of mystery and an unnecessary fleshing out of what's usually best enjoyed in its concise, original form, this box set is so beautifully appointed, and thoughtfully put together... man, if you can afford it, get it.

At the centre of it all is the album itself, on lovely 180g vinyl and the three 7"s that accompanied it (including the tracks 'Cadillac', 'Thunderwing' and the fab 'Lady' – all of which were previously only available as b-sides) – these still exert a command and control on you and your heart rate from the moment you drop a needle on 'em, Ringo's blurry cover-shot all you need to look at, if your eyes aren't shut from trying to hit those notes. And as 'Main Man' spins you out on the last reel, you get in real close with Bolan, you hear where he's at, and you want to stay, and see if he can survive, still now, even as you know where and how this man would end : "is there a sane man anywhere anywhere? / Got giraffes in my hair and I don't care no I don't care, no I don't care / As a child I laughed a lot o yes I did o yes I did / Now it seems I cry a lot / Oh tell me true don't you?". Yeah, I do Marc. You're not a punchline. You're not a wannabe. You're a bloody little pop genius and The Slider is your finest hour. If you're in any doubt, you don't deserve it. A late, breaking contender for reissue of the year. Submit forever again.