On holiday last week I read Grant Morrison’s Supergods. It’s an odd book: a cocktail of blazing-eyed fandom, autobiography and critical history. It’s great at the first two of these, quite poor at the third – a possible problem since the critical history (of superhero comics, and the wider idea of the superhero) is what the book’s built around.

The good stuff first: Supergods is at its best when Morrison is intoxicated by comics, which he is a lot. He riffs creatively on the contrasting covers of Action Comics 1 and Fantastic Four 1, but his best material here is less concrete. Talking about his boyhood favourites – John Broome’s Flash, Weisinger-era Superman, Roy Thomas’ Avengers, Kirby’s New Gods, and Starlin’s “cosmic” Marvel stuff – Morrison’s writing goes into thrilled meltdown. He talks in the acknowledgements about the hard process of editing the book but these sections read like sheer first-draft enthusiasm. I can’t think of anything I’ve read which captures so well the mind-exploding power of comics when you’re the right age to really get hit by them.

One chapter of Supergods is called “Superpop” – reminding me of Nik Cohn’s Awopbopaloobopalopbamboom, that never-bettered story of pop’s searing adolescence. Morrison on form is as near as we’ll get to a comics Cohn, handing down rapid-fire judgements on anything that he remembers to include, with an authority born out of true love.

Of course, for the analogy to hold, Nik Cohn would have had to hit big in a new wave band and ride out the rest of pop’s history playing at the top of the bill. Morrison’s perspective is that of a modern superhero giant, one of the most well-regarded writers the mainstream has ever produced. The problem is that to many external eyes the mainstream comics industry looks fucked – in self-cannibalising decline for coming on twenty years – and Morrison is stuck in the cultural equivalent of the bottle city of Kandor, a place screenwriters and producers visit for a bittersweet while to draw nourishment from its glittering memories and age-old wisdoms.

That’s not to say he doesn’t a) still have one of the coolest jobs in the world and b) do it very well – but it means I take his arguments about the eternal relevance of the superhero with a progressively larger pinch of salt. Sometimes he’s on the mark – talking about the superhero as an idea that will endure forever and the likely immortality of its strongest brands. He’s also right that superhero stories are particularly suited to the comics page. But that doesn’t mean the status quo of superhero comics and films will endure – and Morrison seems conflicted about Hollywood’s current fascination with superheroes. On the one hand he points out – with some justice – that the movies are usually two to four decades behind the comics in terms of their interpretation of top-flight characters. On the other he’s clearly aware that the current health – possibly the existence – of comics Kandor is dependent on a superhero film boom that may well be a bubble. Neither of these really add up to his assertion – towards the end of the book – that “We won. Now what?”

An unconvincing book can still be a good one, of course – you don’t have to agree with Morrison’s theories to get a kick from the way he presents them, and he tells his part in the story – alien abductions, magical summonings and all – with brio and plenty of candid insight into how and why he wrote particular stories. He puts a great deal of stock in cyclical theories of culture and history but he uses them to feed his creativity: most people who talk about 11-year cycles (or whatever) do nothing other than smugly anticipate the next inevitable polarity flip of the trend – Morrison grabs the idea and starts creating comics to fit what he thinks is coming. He reminds me sometimes of Brian Eno – another intensely creative, unorthodox thinker in love with process: Eno used chance and game-playing, Morrison used ritual and magic (and occasionally pharmaceuticals), but they both funneled their discoveries straight into the work.

Deeply creative connectors can make good historians too, no doubt, but the lenses Morrison is using to look at comics – or even superhero – history are too personal and skewed to make the book’s dual identity as history and criticism work. The most obvious issue – Morrison’s somewhat high-handed treatment of Jerry Siegel and Joe Schuster’s claims as creators of Superman – has got most of the negative press. The brushing aside of the Siegel/Schuster case isn’t as depressing, somehow, as the excited intimations that this was part of an inevitable cosmo-mystical sacrifice surrounding the Superhero’s birth.

But there are other frustrating lapses in detail – reading Supergods you’d be forgiven for thinking only Marvel, DC and Image had ever published Superhero stories after the early 60s. In terms of winnowing out the material to cover this makes some sense but it leaves out a lot of the joins in the story. So there’s no Turtles, no American Flagg (the Dark Knight section is screaming out for a mention of this), no Zot! or Nexus (humane, positive superhero comics in the midst of supposed 80s darkness). Factor that stuff in and it blurs the “Dark Age” and “Renaissance” even more – it’s already pretty much impossible to see why Brad Meltzer’s Identity Crisis (Superheroines get raped too!!) is part of the latter not a sleazy hangover from the former. Also, in a book about the world-conquering power of the superhero idea, it’s a shame there’s not more about how its gravitational force was felt in alternative comics – the way everything from 60s undergrounds through Love And Rockets to Eightball seemed compelled to offer some comment on superheroics.

Of course, if you’re reading for Grant Morrison’s freewheeling insights into his favourites and his own life and times, these will seem less than quibbles. And I’d say those are exactly what you should be reading Supergods for. As a critical memoir it’s a joy; as a critical history it’s frustrating and insubstantial.