Terry Gilliam’s directing career thus far has certainly been a fascinating one. For most people, the fascination has been in following the unusual nature of his traject­ory, from the instantly recognisable animations he produced for Monty Python to the translation of this vision into a form of baroque-surrealist live-action cinema so distinctive and influential (Tim Burton?) as to merit the adjective Gilliamesque.

But then there’s another side to Gilliam; he’s a perfect example of a genuine modern auteur, casting and recasting a limited number of enduring thematic obsessions in a series of elaborate and interweaving variations – mediævalist fantasy, Quixotic tiltings at windmills, wounded kings and would-be redeemers – and, underlying all this, a constant concern with the redemptive powers (or not) of the imagination in the face of the crushing literalism of the real world of things as they are.

The Imaginarium of Doctor Parnassus is, seen from this viewpoint, a belated final instalment in a trilogy of films written by Gilliam and actor Charles McKeown that kicked off back in 1984 with the unexpected, and unexpectedly wonderful, riffing on Orwell that was Brazil (still the highpoint in Gilliam’s œuvre to date) and continued in the over-budget and over-the-top shaggy dog shenanigans of that critically lambasted box-office bomb The Adventures of Baron Munchausen in 1988. The intervening couple of decades saw Gilliam channelling the same obsessions, sometimes more obliquely, into more publicly acceptable forms in his Holly­wood films; but now, a quarter century after Brazil, we’re back in the realm of high fantasy, outrag­eously elaborate oneiric visuals and the eternal clash between imagination and reality, truth and lies, good and evil.

The action (if it can be called that) begins in our own version of Eliot’s Waste Land when the immortal Doctor’s travelling theatre troupe-cum-sideshow pitches up amongst the drunken yobs, desperate housewives and frantic shoppers of contemporary London. Parnassus might appear to be vainly casting the pearls of his imagination before such swinish inhabitants – there’s a lovely shot of the Imaginarium parked outside Homebase – but, like Munchausen before him, the ancient showman isn’t quite what he seems; in this case, not content with being a liar and teller of tall tales, he’s a control freak who treats his nearest and dearest like puppets in a toy theatre and a compulsive gambler who has signed away his own daughter’s soul to the Devil (a gravel-voiced and eyebrowless Tom Waits), who gets to collect on her 16th birthday.

Parnassus (touchingly played by Christopher Plummer), even with his perambulating wagon of pop-up wonders, can’t save us, being merely the wounded Amfortas to Waits’s cunning Klingsor. Luckily, Old Nick is a betting man, too, and in one final wager the two old rivals go head to head in a first-past-the-post compet­ition to capture five souls. But the drunken Parnassus can’t even lay off the sauce, let alone rustle up any punters or put on an entertainment likely to snare a few souls.

Enter Heath Ledger’s white-suited Parsifal-figure, the distinctly dodgy Tony, who has a good line in patter and a glad eye for Valentina (child-woman-model Lily Cole, quite as bizarre-looking as anything in Gilliam’s own Imagin­arium) – will he be able to save Valentina and Parnassus? And in doing so, will he save himself? It’s hard to figure out, in this fallen world, precisely who is most in need of redemption; some would say it’s also hard to care.

Parnassus seems, in a way, to offer a darker vision of the old opposition of imagination and reality than did Brazil (in which the former is brutally snuffed out by the latter) or Munchausen (in which it exults triumphantly in its very status as fiction) because, nowadays, things are more complic­ated. The Imaginarium is a dangerous contraption, an ana­logue of cinema itself; it’s essent­ially a theatrical flat on wheels which opens, wardrobe-like, on whatever personal Narnia the visitor carries around in his or her head. It’s a dream factory, evoking a whole history of illusionist technology – from itinerant magic lanternists to the onslaught of Avatar’s 3D worlds – and suggesting that such wheezing engines of wish-fulfilment and escapism are all smoke, mirrors and snares.

By the film’s conclusion, we’re left wondering whether the ascendency of imagin­ation that Gilliam/Parnassus, the commercial cinema and, indeed, our patho­logically fantasy-prone society have encouraged is in fact the primary reason for the terrible state that the characters – from Par­nassus himself to the ambiguous Tony, whose illusory self-image has run away with him – and by extension the audience, are in. Tellingly perhaps, even Gilliam’s usual flood of fantastic imagery seems at times to run dry in this film; the mindscapes unleashed by the various visitors to the Imaginarium are strangely, well, unimaginative – this kind of vision of personal fantasy writ very large has been done better in The Simpsons (just think of  Homer’s daydream visit to the ‘Land of Chocolate’ for starters).

In the end, Doctor Parnassus is a fascinating failure that’s a damn sight more interesting to think about than to actually sit through, its fantastic gambits – like those of the Doctor – ultimately delusions. Perhaps Gilliam is suggesting that we should all be moving along now, out of the cinema and into the real world, forsaking the lure of the Imagin­arium for the Homebase just across the retail park.