Sky doesn't make many dramas, but when they do they make them well. Going Postal is Sky's latest Terry Pratchett adaptation, a big budget extravaganza in two parts, filmed upon elaborate sets and exquisitely costumed, that lovingly recreates Pratchett's weird and wonderful alternative universe of Discworld.

Richard Coyle stars as confidence trickster and irrepressible charmer Moist Von Lipwig, spared from the gallows to perform the equally lethal task of reviving the Ankh-Morpork postal service. Postmaster General is an office with a one hundred per-cent mortality rate, with several fingers of suspicion pointing firmly in the direction of ruthless entrepreneur Reacher Gilt (David Suchet) who will stop at nothing to impose his Clacks communication system upon the populace.

Frantic, funny, romantic, silly and frequently touching, Going Postal delivers in many, many ways.

Nearly always it's the quiet ones that surprise you with their anger. Terry Pratchett's delightful series of surreal Discworld novels have long bewitched readers. Pratchett novels have always acted as gentle satires of our world, but Going Postal, the latest of his novels to be filmed by Sky was, by Pratchett's standards at least, monumentally angry.

Porcine bankers, the celebration of corporations, the moral vacuity of the concept of victimless crime and, er, the incorrect use of apostrophes, were all fed into the novel that was the source for this Sky adaptation. The anger was mollified for family viewing - but only slightly.

David Suchet, almost unrecognisable as a villain who resembled an ageing, heavy metal star, played Reacher Gilt - the rapacious owner of Clacks, a network of semaphore towers which are Discworld's take on the internet.

This was a man who had taken advantage of a banking crisis to move in and steal Clacks from its inventor. Gilt was enraged when the patrician Lord Vetinari (Charles Dance) pardoned conman Moist von Lipwig (Richard Coyle) on the understanding he revive the Discworld's postal service to provide some competition to Clacks.

Part of the glory of this fabulous chunk of entertainment was that Sky eschewed CGI in favour of lavish sets, constructed with lashings of sparkling invention. Going Postal looked amazing. Luckily, everything else about the production was dazzling too.

Coyle was roguish but sympathetic, and Andrew Sachs, as his assistant, bumbled along like a cross between his Fawlty Towers duffer Manuel and the original grandfather from Only Fools And Horses. Claire Foy, as Adora Dearhart, smouldered convincingly.

With its teatime scheduling and raft of fabulously named characters, you could have been forgiven for supposing Going Postal was intended as a family-friendly fairy tale. But there was a delicous darkness about this handsomely mounted adaptation of the 33rd novel in Terry Pratchett's Discworld series that definitely needed a parental advisory sticker.

Corrupt bankers, the mindless adulation of progress, the absurdity of 'victimless crime'; this was Pratchett aiming two barrels at a galaxy of pet hates - including, delightfully, missing apostrophes - all gathered around the yarn of conman Moist von Lipwig and the accursed Ankh-Morpork post office. And he was well served with a richly rendered visualisation of Discworld, from avalanches of unsent letters to a menagerie of curious characters, that made for a Delicatessen-style visual feast.

And you could have a lot of fun wondering where Dickens and Tolkien ended and Pratchett began, such was the weight of literary influence. But it went deeper than that. Drawing on first-class performances - Richard Coyle excellent as a believably conflicted von Lipwig; Claire Foy a sneering delight as Adora Deerheart, the perfect anti-love interest for the perfect anti-hero - Going Postal sent out a heartfelt plea to celebrate the individual over the corporate, the human over the machine. On that score Going Postal was a special delivery.

Terry Pratchett's Going Postal, a two-part special from Sky1 which concludes tonight, had a pretty distinguished cast too. Presumably the thesps in question were attracted not just by the money, but also by the always-welcome chance to don some eccentric facial hair and shout a lot. Then again, they could even have been attracted by the script - because the programme is enormous and imaginative fun.

Needless to say, with its origins in a Pratchett novel, the imagination does tend to the bonkers. Richard Coyle plays Moist von Lipwig, a con man rescued from hanging by the mysterious Lord Vetinari (Charles Dance, salt-and-pepper beard and moustache). He was then given the job of reviving the Ankh-Morpork Post Office, much to the fury of the man who runs the Discworld equivalent of the internet, Reacher Gilt (David Suchet, Fu-Manchu moustache, beard and eye-patch). Moist's allies include the elderly junior postmaster Mr Groat (Andrew Sachs, huge moustache) and the toothsome Adora Belle Dearheart (Claire Foy, no facial hair but obviously enjoying putting Little Dorrit behind her by smouldering sexily and generally carrying either a cigarette or a riding crop).

With these - and plenty more - elements in place, last night's episode rattled along nicely, easily passing the key test for all programmes that seek to create another world: we gradually stopped noticing how mad that world was. By the end, in fact, it seemed perfectly logical that a seven-foot clay robot should have persuaded Moist to confess that he'd been responsible for the forged cabbage bonds which ruined Adora's family - while back at the Post Office a young man obsessed with pin-manufacture was attacked by a flying monster.

The cosmology of Going Postal is perhaps best described as pre-Newtonian. The Earth is flat and rests on the back of three humungous elephants, which in turn rest on the back of a giant turtle. This, as Terry Pratchett devotees will know, is Discworld, an extensively chronicled alternative universe in which the knowing joke is one of the fundamental physical forces. Those who aren't Pratchett devotees might be pleasantly surprised by Going Postal, which is so nicely done that it makes a proselytising case for the author's distinctive imagination. Richard Coyle plays Moist von Lipwig, a con-man and fraudster who is saved from the gallows to bring a bit of healthy competition back to the communications industry in Ankh-Morpork. Charles Dance's Lord Vetinari invites him to revitalise the derelict postal system in order to give consumers an alternative to a kind of steampunk telegraphy system, run with monopolistic greed by the villainous Reacher Gilt.

Moist has no intention of doing any such thing, particularly since he soon learns that all his predecessors have died trying. But as he tries to raise enough funds to flee, he inadvertently invents postage stamps - and begins to be haunted by the consequences of his former frauds. He also has the problem of getting away from his probation officer, a giant golem called Mr Pump, who eventually brings him into contact with the love interest in the piece, a young woman who runs a golem rights consciousness-raising group. It looks terrific and is full of good jokes, including a running gag about Stanley, one of the junior postal clerks, who is an obsessive pin collector. In an attempt to make small talk with him, Moist mentions that he's seen Pins Monthly on the newsstands. "That rag is for hobbyists," hisses Stanley. "True pinheads only read Total Pins." There are appropriately scary villains, some lovely special effects, including a tsunami of undelivered letters that pursues Moist through the corridors of the old Post Office, and just enough real feeling to make you care about what happens next. One of the opening credits read "Mucked about by Terry Pratchett", but neither he, nor they, mucked it up.

Sky has said it's trying to build a reputation for drama, and it's certainly going the right way about it. This adaptation of Sir Terry Pratchett's 33rd Discworld novel concludes tonight and it's a gloriously-realised, filmic vision of the fantasy universe.

It follows Sky's recent adaptations of Pratchett's Hogfather and The Colour Of Money, as well as bestsellers by Martina Cole and Chris Ryan. And with 20 more feature-length films in the works, all based on novels, Sky is definitely going to be giving the other channels a run for their money drama-wise.

Tonight opens excitingly, with the Ankh-Morpork post office in flames and under threat of closure from a flying banshee. The stellar cast is headed by Richard Coyle as conman-turned-postmaster Moist von Lipwig and Claire Foy as Adora Belle Dearheart.

But it's the spectacular scenery and special effects that make this an absolutely first-class show.

Sky1 continues its love affair with the fantasy world of Terry Pratchett with this lavishly put-together and thoroughly entertaining two-part adaptation of another of his Discworld comic novels. Coupling's Richard Coyle is low-rent conman Moist von Lipwig, who is saved from the scaffold to revive Ankh-Morpork's moribund post office. It's a poisoned chalice (he has serious competition from a rival company), and Moist's attempts to escape are regularly thwarted by both a clay creature called Mr Pump (like Marvin the Paranoid Android, without the doom-laden introspection) and Moist's own growing feelings for the equally theatrically named deposed heiress Adora Belle Dearheart (Claire Foy). The story fairly rattles along with a host of well-known faces adding extra colour, the special effects are neatly integrated, and there are some distinctly spooky little touches to add a frisson of fear. Concludes tomorrow.

Sky may not have the resources to churn out top home-grown drama on a routine basis, but when it does decide to throw its weight behind a production, as it's done for this latest Terry Pratchett Discworld adventure, then it certainly does it in style.

Shot in HD, and with a fabulous British cast that includes David Suchet, Richard Coyle, Charles Dance, Claire Foy, Andrew Sachs, Steve Pemberton and Tamsin Greig, this Bank Holiday two-parter (concluding at the same time tomorrow) is a typically outlandish Pratchett tale about a lifelong con man who's given one last chance to avert the death sentence. The deal? He must take on the seemingly cursed task of trying to rescue Discworld's Post Office, under threat from their equivalent of the internet.

Sky's third venture into the cult fantasy world of Terry Pratchett (after Hogfather and The Colour of Magic), Going Postal again does justice to the author's peculiar vision. The weirdness of Discworld is appropriately captured in a tale of love and redemption which blends satire, humour and drama. It tells of a con artist, Moist von Lipwig (Richard Coyle), forced to atone for his crimes by taking the cursed role of postmaster at the dilapidated Ankh-Morpork's post office. The job puts him in the firing line of Reacher Gilt (David Suchet), who runs a rival delivery service, but also leads to an encounter with Adora Belle Dearheart (Claire Foy). Concludes tomorrow.

A bad boy goes postal

Richard Coyle plays swashbuckling villain Moist von Lipwig in Sky1's grand adaptation of Sir Terry Pratchett's Going Postal, which begins on Sunday. The actor explains to Lisa Williams why Sir Terry's books have such a wide appeal, what it was like playing a baddie, and why he felt like he was covered in clingwrap for the duration of filming.