Ah, the enigma that is Glenn Danzig. On one hand, he is the trash-culture savant whose canny mix of melody and B-movie melodrama helped propel The Misfits to become one of the most recognisable punk brands of the last 30 years. On the other, as the purveyor of particularly lumpen base metal, he is so lacking in self-awareness that the endless YouTube parodies and homoerotic caricatures seem almost cruel in their fish-meets-barrel goading.

And while his former band-mates have had a fair old whack at in his absence squandering The Misfits' legacy, there is still enough mystique surrounding them to guarantee the overwhelming response to this tour. Yes, it's a celebration of his eponymously monikered band's 25th anniversary, but the added bonus of Danzig revisiting some choice cuts from his first band's back catalogue with Misfit guitarist Doyle von Frankenstein was the draw that had the Roundhouse bursting at the seams.

Indeed, like barnacles clinging to a rusting hulk that has just dropped anchor for the first time in a generation, the detritus of a quarter-century of alt.culture was here: hardcore kids of all ages – some squeezing their beer bellies into carefully preserved straight-edge shirts; their female counterparts in off-the-peg Rosie the Riveter or Bettie Page garb; skinheads; goths; crust punks; unembarrassable metalheads in Limp Bizkit T-shirts and their grungier forebears in cargo shorts and motorcycle boots. As if to underline the underground-in-amber theme, an aging punk with liberty spikes stood outside 'poncing the queue', a beanie held out to receive spare change to pay for his ticket. A regular sight outside gigs in the 90s, I think this was the first time I'd seen one of these characters since the turn of the millennium. I couldn't help but admire his old-school chutzpah.

From the balcony, it looked like Danzig the man had cloned himself to fill the musical roles in Danzig the band, as he was preceded to the stage by the three slightly hairier versions of himself in their black jeans, cut-off vest and bared-bicep uniforms. Musically, however, their contributions were less regimented. Newer songs 'Skin Carver' and 'Hammer Of The Gods' chuntered along in third gear, punctuated occasionally by affirmative grunts from Danzig and a super-sized serving of harmonic squeals from guitarist Tommy Victor. At times, it felt more like a loading screen from Guitar Hero than an actual concert.

“OK, we're done with the new shit. We're only playing old shit from here on in.” This received the biggest cheer of the night thus far, followed quicky by another roar when the opening notes of 'Twist Of Cain' rang out. Yes, it's a wholesale filch from Led Zep's 'In My Time Of Dying', but as statements of intent go – it being the opening of Danzig's first album – it's a very convincing one, and did plenty to raise the stakes here. The thundering 'Am I Demon' followed – and when the roiling crowd turned the plaintive "Am I beast or am I human? Am I just like you?" bridge into a roof-raising terrace chant, it was clear that, contrary to initial impressions, something memorable was taking place.

Almost bloody-mindedly, Danzig then dusted off his gothic torch song 'Blood And Tears', a track they haven't played in twenty-odd years, as if to say: "Yes, I am the king of this juggernaut of metal, but I've a sensitive side, too – I've written songs for Roy Orbison and Johnny Cash, goddamnit!" And the crowd, now in the palm of his hand, indulged him unequivocally. Even in the rarified air of the balcony, grown men with their shirts off tumbled over seats (and on top of fellow patrons), swaying and hollering along.

"Where's my monster man? I need my monster man!" demanded Danzig, announcing the arrival of Doyle to wind back the clock even further. As the guitarist stomped on stage to comedy Frankenstein sound effects, my companion reared back in his seat: "Jesus Christ, he's fucking massive!" Even taking his giant Boris Karloff boots into account, Doyle easily dwarfed his singer, and when he thrashed at his guitar over the next five songs, he looked more like a gorilla stripping bark off a sapling. 'Death Comes Ripping' came ripping, of course, while Astro Zombies immediately transported me back twenty five-odd years to a teenaged bedroom existence of cheap cider and Evilive on a TDK D90. And 'Last Caress', the song that rocketed The Misfits out of their cult cul-de-sac and into the limelight thanks to Metallica's ... Garage Days... cover, caused the teeming throng below me to threaten to engulf the stage like a tsunami. It was around this point that I realised the protective nature that I, and many others, have about hardcore punk – its folk-culture semiotics and socio-political aspirations - cannot reasonably be applied to The Misfits. Firstly, hearing 3,000 people bellow out "I turned into a Martian – wooa-ooa-ooah!" is something I'm hugely glad to have experienced. It's how this song should be heard. Secondly, they're singing about turning into Martians, for Chrissakes! This is about as far from the 'Does Crass belong in an art gallery?' argument as you can get. It was magnificent – spinge-tinglingly so - and the addition of Von Frankenstein was pure alchemy.

As Doyle clomped off stage, Danzig apologised for having to cut their set short (contrition from Danzig? This was something, like the massive smile on his face during the Misfits section, I never thought I'd witness), and 'Soul On Fire' and 'Mother' were offered as consolation. This is a double-whammy most bands would kill to have in their arsenal but, after what we had just seen, it couldn't help but seem slightly anticlimactic. 'Not Of This Earth' kicked off the encore after a very brief break, then Doyle returned for two more songs. Danzig teased the crowd with the possibilities of hearing 'Bullet' or 'London Dungeon' – even when giving the audience what they want, he still holds something back – but then decided on 'Night Of The Living Dead' and 'Die, Die My Darling'. The latter was particularly electrifying – a staccato jab of gothic theatre that descended into a maelstrom of feedback with Danzig, arms aloft, howling invocations at the moon, all of it sounding as vital and dangerous as it did three decades ago. It was a stunning finale, and the night should really have ended there. However, the band, giddy with their accomplishments, broke the spell by coming back on stage to take a quick iPhone snap in front of the still-chanting, still-hungry crowd. It would be churlish to deny them that pleasure, though – this, apparently, was a special night for everyone involved.