In the way of metal festivals, there’s Ozzfest, Metalmania, Download and Donnington, Wacken Open Air, and then there’s the Unholy Alliance. Laying waste to America and Europe for the second time last year, it was promoted as ‘the world’s heaviest tour’, which could well be true. Thine Eyes Bleed, Children of Bodom, Mastodon, Lamb of God and a re-united Slayer all had a part to play in the carnage, which finally makes its way onto a DVD. Or at least, bits of it do.

Filmed at the 20,000 capacity General Motors Place in Vancouver, Canada, The Unholy Alliance Chapter II: Preaching to the Perverted is a half-complete replay of the night’s concert. Slayer’s easily recognized logo is scrawled across the front in large, blood-red font, and their full show is indeed contained within, to be enjoyed in its full headbanging glory, but the snippets from the other acts on the tour are so tantalizingly brief, and sometimes poorly thought-out, it’s almost as if the makers of the DVD are trying to make you even more jealous for not being there to experience the real deal. Musically, of course, it doesn’t get much better than this – some of metal’s biggest names are on the bill, and in fine form, too, so the main fault with The Unholy Alliance is the compilation.

Ontario’s Thine Eyes Bleed look a hell of a lot like a younger incarnation of the very headlining band, a problem not helped by the outfit’s bassist being the brother of Slayer’s Tom Araya. Nonetheless, they contribute a solid, if forgettable number, “Dark White”. Children of Bodom, who trek it out all the way from Finland, get a more generous preview of two songs – “Angels Don’t Kill”, practically a ballad by their manic standards, and single “In Your Face”, far more effective in a live setting than on its tepid, banal studio counterpart. Drummer Jaska Raatikainen in particular keeps the song swerving through a mindlessly direct refrain (“I don’t give a flying fuck, motherfucker!”) with some clicking double-kick footwork.

Current metal stars Mastodon shed their elaborate sonic elements almost entirely in favor of a more straightforward performance here, winning you over with the droning force and tight band unity evidenced in “Capillarian Crest” and “Crystal Skull”, both from last year’s critical darling Blood Mountain. There can be no excuses, however, for a hugely disappointing oversight when it comes to the inclusion of one Lamb of God. At the height of their success (latest effort Sacrament was one of the fastest-selling metal releases of 2006) and with a fearsome reputation as a live act already established, the presence of just one song on the DVD seems grossly unfair. Fortunately that cut, “Vigil”, has enormous staying power. Frontman Randy Blythe troops onstage smoking a joint, and proceeds to give an absolutely possessed vocal show that burns its way into your memory. His screeching, bug-eyed intensity is matched by the stomach-churning groove his bandmates work up, transforming the floor into a frenzied ‘old school circle pit’. Not only is it a highlight, it shows up every other band on the tour.

But that’s not the main attraction: Slayer’s ten-song show is. Now well into their 40s, there’s no doubt every band before them on the line-up was influenced by the mighty Californian four in some way, as well as an entire generation of new practitioners of heavy music, both obscure and famous, but it seems rather like Slayer may be – dare we say it – getting a bit past it. Putting the night’s opening acts before them is a move that backfires, as it only sets expectations higher for the former after an hour of younger contenders. Their performance is also hampered by a rather poor setlist overall: a measly two numbers from their powerful comeback album Christ Illusion, none from the three before it, and only one from the band’s undisputed peak, Reign in Blood. This leaves their cuts to be mostly pulled from their late-eighties/mid-nineties midtempo output.

That said, the venue’s lighting works wonders for them, drenching the band members in blood red and godly strobes, inverting crosses on the demonic opening riff to “South of Heaven” and spraying pentagrams all across the floor, while returned sticksman Dave Lombardo is the star of the show… His lightning fast fills are ever on top of the twisted thrash. It is kind of a comical sight to see chief songwriter Kerry King bobbing his bald head up and down with the music, but him and Jeff Hanneman are still as talented a pair of guitarists as in their heyday. Instrumentally, Slayer is still top-notch, but their warhead is losing some of its destructive capacity because their main weapon, vocalist Tom Araya, is dulling with age. Having just had gall bladder surgery, his versatile, terror-inducing scream isn’t what it was, and he resorts to just shouting the words instead of putting much emotion or conviction behind them. The speed of the faster numbers leaves him behind, and he gets more tired as the concert goes on.

Of their songs, the oldest tend to fare the best – that uneasily building intro to “Hell Awaits” is still staggeringly sinister, leading in to vintage blast “The Anti-Christ”, which is here rather below par, but then the band rip through “Angel of Death”, finishing their Unholy Alliance on a high note. A classic that caused Slayer more controversy than any other, Lombardo’s drumming pelts out at warp-speed, the twin guitars roar with venom, while a backdrop image of Nazi doctor Josef Mengele himself ensure this slice of essential thrash is still genuinely scary. That’s kinda re-assuring, too.

The unmistakable feeling that this DVD is little more than a cash-grab arise again with the bonus features; unless you’re interested in fans using a lot of swearing to explain why Slayer is the best, the ‘Behind the Scenes’ segment isn’t really worth bothering with, and the band interviews are flat-out stupid. It’s easy to see the members involved are having fun, but it’s difficult to distinguish what the hell Mastodon or Children of Bodom are even talking about, and that makes for frustrated viewing. With a little more effort put into its transition from stage to television, The Unholy Alliance could have been truly fantastic. Don’t get me wrong; it’s very valuable to see a concert such as this, no matter in what form, but as it is this DVD screams missed opportunity at nearly every turn.