Why has the boy wonder of British poetry grown up into a fussy stargazer?
Here is one story-line. Simon Armitage comes from Huddersfield, grew up in West Yorkshire, read geography at Portsmouth Poly, did a social work certificate (plus thesis on TV violence) at Manchester, and worked as probation officer till glamour struck in 1989. His first collection, Zoom, arced him into orbit as, at 26, the archetypal streetwise poet - a wonderful new voice, bewitching people who thought poetry had nothing to do with them, and also distinguished poets. "Energy directly from life and the living language", wrote Carol Ann Duffy. "A muscular, elegant language of his own", wrote Peter Reading, "with the benefit of unblinkered experience."

Zoom made real-life speech and activity the centre of a tungsten-tough poetry of deadpan flair and casual, leave-it-there humour. The cleverness was in the angle. Armitage wrote about grow-bags, walk-in wardrobes, brake- fluid, cashing the Giro, dumping granny at the old people's home. He struck a Kung-Fu palm along the anatomy of human relationships: their inequalities, their inconclusiveness.

Two years later, his first Faber book, Kid, consolidated his name for technical virtuosity, black humour ("Hillsborough was a different ball game"), double-edged musings on living with a woman: "your favourite dress/is damp and unironed;/you haven't a stitch to wear/and I am to blame." Very Yorkshire; very Simon Armitage. The voice emanated a self-deprecatingly cocky self-centredness. The title poem is spoken by Robin; "Batman, big shot... I'm the real boy wonder".

Kid's first poem features a murderer. "Brassneck" is a football pickpocket ("Down in the crowds at the grounds where the bread is:/the gold, the plastic, the cheque-book the readies."). It had brilliant rhyme ("bread is/readies") and a winning confidence. But some (poets, mainly) found it less convincing than Zoom.

Armitage began TV work. His third collection introduced a new note: an anoraky obsession with series. A Book of Matches (punning between Swan Vestas and matters matrimonial) was a sequence of self-portraits, plus poems on his wedding. The series felt contrived and tricksy, the wedding stuff banal. Poems began to seem form-led; praise came mostly from non- poets. (There's nothing wrong with that - poets don't write for each other - but it was a change.) "A firework display of technique, versatility, and passion", wrote one reviewer. Poets went rather quiet.

Two years later came Dead Sea Poems: about stray dogs, goalkeepers and Christ, ending in a long intricately-crafted poem called "Five Eleven Ninety Nine", on the millennium's last Bonfire Night. Some people thought it brilliant. But, like the Matches sequence, it was based on one bright idea, which the poem seemed written to.

So, mainly, is his new volume, CloudCuckooLand (Faber, pounds 7.99). It too depends on sequence. It has three parts: 14 poems (a first section called "Thin Air"), then 81 small verses on the constellations. "Simon has been probing the night sky with a telescope", says the blurb. You can't help feeling he bought the thing to write the book. These poems reduce the most cosmic of themes to private concerns. Most make the same move: the constellation-figure (Pisces, Centaur) impinges on, or images, "us" or "me". The poor old stars have mirrored the human lust for pattern since Babylonian times. Even as image of a relationship, there must be something more to (say) Scorpius than this:

The weapons we used for tearing each other in two/ were dipped to the hilt in a secret potion, an oil/ for the stemming of blood and the cleansing of wounds./ This solution, applied to ourselves, was a poison.

Oodles of charmed technique here. Double meaning ("solution"); liturgical resonance; pomposity-speak sent up ("applied to ourselves") - but it's all so solipsistic. Can the fifth collection from a high-profile poet of 34 not use the heavens as a bit more than the catalogued parts of its cosmological mirror? You imagine him ticking them off. ("Ursa Minor down and 64 to go...")

Last comes a commissioned play that features star-gazing and cannibalizes the idea behind "Five Eleven Ninety-Nine". After the millennium's last bonfire, here's the last eclipse. It wants to be apocalyptic but fails to touch the emotional and imaginative wealth of its subject - like writing a cheque on a dead bank.

So there's one story. Paul McCartney after the Beatles. A brilliant poet becoming progressively unpersuasive. A trajectory that disconnected him from his first zest. A reputation that comes, like the stars' light, from that faraway first book. If that is the story, so what? Armitage does TV and radio work. Literary sniffer-dogs love the aura. "England's leading young writer", they murmur. He sells, he looks the part, is a charismatic reader, takes poetry to places other poets don't reach. Does it matter if the work seems less and less convincing?

Well, yes: terribly. You hear about poets' jealousy, but though they care about spotlight and cash, they care most about work. You are only glad of a gift like Armitage's. You want to see where he's taking it, be excited and convinced.

So here's an alternative line. From his first interests (human geography, sociology, violence) came his wonderful knack, central to his work, for visual description with despairing social resonance. Since Zoom he's been exploring. That obsession with pattern may seem artificial but is connected to his brilliant patterning of rhythm, of rhyme. He's got to follow this: it's where he comes from. In developing, you invest in poems which chase new things in yourself, even though they may not, each time, make a great book.

Armitage's yen for pattern works best, lyrically, when set against human chaos. But he's drawn to cosmic themes. Religion yesterday, cosmology today: I was in a minority of one for admiring all of Dead Sea. I thought it took his own self-aridity and made it represent, brilliantly, his whole generation. From not-feeling at the end of a marriage came an elegy for the death of sacredness.

Maybe he's doing it again. The only real poems in CloudCuckooLand are the "Thin air" section. (They would have made the powerful kernel for a slower, feeling-led collection.) "Mojo" suggests meaningfulness is over: "We saved no more from the box of tricks/than the empty box". "Gift Horse" is a James Herriot-ish allegory on the death of value: of valuing the life we're given.

Its coat is a quilt of sweet-itch, rain-scald,/ gall, patches of skin, the workings of lice,/ and sheep-ticks barb its underside, and flies/ go wild for the essence it weeps, the scent/ from under its tail and between its legs./ Its thoughts are in the Mariano Trench...

Maybe this is where Armitage is really at. When led by pattern, not life, he loses touch with the blood of his gift. But is he making poetry out of that very loss: taking a cosmic subject and proclaiming the triviality of human response to it at the end of a millennium? The CloudCuckoo illusion is imagining we can mean, any more.

Instead of a poet who has lost his way, you get the priest of a generation that has lost value, lost meaning. Take your pick.