Ruining the screen conversion of the original book version of “Good Omens,” which tumbles through the eons into a modern tale of Armageddon, would have been easy. A magical creation of Neil Gaiman and Terry Pratchett, the book was a wild concoction of fancy and word play and mythology and theology. Screwing up the plot, taking just one misstep with the pacing, or casting clunkers as the demon Crowley and the angel Aziraphale … so much could have gone wrong, and, based on the screen history of much-loved books, the portents were uneasy. But I can report that the sumptuous six-part series, with script in the hands of Gaiman and an able direction by Douglas Mackinnon, is not only faithful, but entertains and delights throughout. Michael Sheen, always at least competent, acts a blinder as Aziraphale, and David Tennant is even more brilliant in the role of Crowley. A stellar, on-song supporting cast, rousing music from David Arnold, and ravishing scenes from cinematographer Gavin Finney, all lift the dominant two roles into a minor triumph of film-making. I’d forgotten how imaginative the original book was, imbued especially with Pratchett’s oblique sense of humour, and the galloping plot development makes for a watching treat. Go no further, viewers.