In my heart I believe that Michael Sheen will never be better than he was as Liz Lemon’s “settling soulmate”, Wesley Snipes, in 30 Rock; a character who deserves to be lauded down the ages for the indescribable awfulness he created around a handful of zingers and a terrifying look of bright-eyed certainty.

In the new Amazon miniseries Good Omens, as the soft, fluttery angel Aziraphale, he pulls off the feat of making goodness watchable and fun. Both Sheen and (a miraculously non-manic, given the potential of his part) David Tennant as the demon Crowley are wonderful in the six-part adaptation by Neil Gaiman of the much-loved fantasy novel he co-wrote with Terry Pratchett in 1990. Their chemistry is a joy, even if the banter they are given is often stale or overegged. (Crowley’s opening line is an uninventive riff on the idiocy of God putting a tree of fruit and “a big Do Not Touch” sign on it in the Garden of Eden and expecting things not to go wrong.)

Aziraphale and Crowley’s unlikely friendship, formed over the 6,000 years that have elapsed in this version of Earth’s history since Crowley got Eve to eat the apple, is the heart of the book and now the miniseries. Confronted with the news that the apocalypse is about to begin – and Crowley delivering the satanic baby that will kick it all off in 11 years into the care of the satanic nuns who will swap it with an ordinary newborn – they are horrified. Both have got too used to the comforts of Earth to want them destroyed. “No more fascinating little restaurants where they know you,” says Crowley, as he tries to persuade his friend he won’t resist a divine plan by averting Armageddon. “No more gravadlax with dill sauce. No more old bookshops.” But they team up to prevent it – Crowley by getting a job as the child’s nanny, Aziraphale as the household’s gardener. The only problem is, as they realise at the end of their 11-year stint of normalising Beelzebub’s offspring, the nuns mixed up the babies. They have been guarding the wrong child.

Off we go into a maelstrom of adventures, misunderstandings and tangles with witches and witchcraft, involving Gilliamesque levels of invention, puppetry stylings, disguises, pyrotechnics, extravagant costumes, CGI curlicues and a general sense that neither kit nor caboodle has been spared in the construction of this entertainment.

It doesn’t quite work, because it doesn’t quite disguise the fact that beneath the razzle-dazzle, every character apart from the main two is tissue-paper thin. This is particularly true of the female parts (Frances McDormand as the narrating voice of God aside), a historical weakness in the fantasy genre you might have expected Gaiman to take the opportunity to shore up. When both Crowley and Aziraphale are offscreen, things fall flat. In fact, a distinct sense that everyone is just marking time until they come back creeps in (albeit alleviated by the occasional appearance of Jon Hamm as Gabriel, nailing every fleeting moment he has as Aziraphale’s shit-eating, Armageddon-happy boss).

That sense isn’t helped by the perpetual signposting of gags, overly faithful reproductions of the original dialogue (what skips along when read becomes laborious when spoken) and the repetitive nature of many scenes. God is most frequently heard describing what is coming up, what is happening on screen and what has happened. In the first episode alone, the swapping of the babies takes for ever to complete and is further drawn out by an illustration using a card trick of what has taken place. Similarly, the hellhound scenes are told as well as shown and the payoff is given semaphore, flares and a spotlight to guide it in. There’s omniscient, and then there’s redundant, OK?

Good Omens was brought to the screen – after languishing in development hell for decades, gaining the reputation of an “unfilmable” book – in fulfilment of Pratchett’s last wishes. It is perhaps an understandable sense of duty that has prevented Gaiman from making as free and as fresh an adaptation as he might have under other circumstances – fleshing out minor figures, and bringing the themes alive with more modern touches than Crowley’s devilment now including the invention of the selfie. At the same time, his central involvement as writer, adapter and executive producer has, inevitably, diluted and displaced the Pterryness (which is always a more gleeful thing than the Gaimanesque). It is a shame that Good Omens’ advent on to our screens at last feels like such a wasted opportunity.