It’s often overlooked that Douglas Adams’ career very nearly didn’t happen at all, despite a promising start. As a youngster, he had one-paragraph stories published in his beloved Eagle comic: at Cambridge, he gradually infiltrated Footlights and made a name for himself as a comic writer and performer. On graduation, he found himself with an impressive patron: Monty Python’s Graham Chapman. Together, the pair worked on Chapman’s autobiography, the sketch show pilot Out of the Trees (1976), and an unmade US TV special for Ringo Starr. Adams was even enlisted for tiny roles in the Pythons’ final BBC series (1974). But there was no escaping the fact that Chapman had fallen into a boozy rut, and the partnership was doing Adams no good.

On detaching himself from Chapman, he took a variety of non-writing jobs to keep afloat, but was beginning to get desperate. He needed to find an idea to accommodate his own rather peculiar writing style quick, or else give up on writing altogether. Salvation came when he suggested to Radio 4 producer Simon Brett that he could write a science-fiction comedy called The Ends of the Earth, in which the planter came to an entirely different end every week. In the event, the first such idea he dreamt up seemed to have promise, and he stuck with it.

Adams had first considered that someone should write The Hitchhiker’s Guide to the Galaxy while lying drunk in a field in Innsbruck. At least, that was the anecdote he repeatedly trotted out, until by his own admission he couldn’t recall if there was any truth in it or not. Indeed, Adams was given to retelling favourite stories ad infinitum, both in his writing and in public. He was honest to a fault about how hard he found the act of writing, and was legendary for his extraordinary ability to miss deadlines. Perhaps this explains his tenaciousness in returning to Hitchhiker’s, reworking the material for a series of novels, a TV series, a computer game and now, at long last, a feature film. Having found a niche for his style, ideas and humour, it became irresistible to reuse it endlessly – always declaring that each new outing was definitely the last. There’s also the fact that his success brought him great fame, enabling him to indulge his tastes in travel, guitars and Apple Mac technology (and to spend time developing the celebrated h2g2 website, effectively a real-life online version of the fictional ‘Hitchhiker’s Guide’). Certainly, this can’t have motivated him to hone his writing skills with any discipline. If one were feeling uncharitable, one might say that as a writer, Adams could be lazy, and his success only made him lazier.

Hitchhiker’s was always going to be a difficult beast to turn into a film. In general, major films have rigid structures, charting the quest of the main characters and building to a satisfying climax. The events of Hitchhiker’s are set in motion by the destruction of the Earth early on, with nothing climactic enough to ‘top’ blowing up a planet held in reserve. In early incarnations – the radio series, books, the TV version – that wasn’t a problem: there was no climax, simply a picaresque series of episodes and tangents. But it’s been just one of the hurdles facing the film.

In fact, the journey of Hitchhiker’s to the screen has been a saga in its own right. In the wake of the BBC TV adaptation, with which Adams was deeply unsatisfied, a US television remake was on the cards, but came to nothing. Adams first sold the film rights to Columbia in the early Eighties, for a handsome fee. He decamped to LA to pen a screenplay, with Ivan Reitman – fresh from directing army comedy Stripes (1981) – set to helm it. But when Adams submitted a script almost twice the length of standard Hollywood screenplays, Columbia baulked. According to the writer, Reitman himself failed to understand the material, feeling that the Ultimate Answer being revealed as 42 might be ‘an anti-climax’. Instead, Reitman elected to make Ghostbusters (1984), a massive global hit.

The project stagnated, with other writers brought in to work on fresh drafts, which left Adams aghast. Rocky Morton and Annabel Jankel, best known for the pilot of the cult Channel 4 show, Max Headroom (1985), were at one point lined up to direct. Monty Python’s Terry Jones had always shown an interest in the project, but never got a shot at it of it. Instead, Adams’ own interest was revived when he became friendly with Mike Nesmith, media mogul and ex-Monkee. At great expense, Adams bought the film rights back from Columbia, and developed a new script in consultation with Nesmith. This time, James Cameron was mooted as a possible director.

The late nineties saw Adams living in America again, back working on the film adaptation, with something approaching obsessive desperation. This time the rights were sold to Disney, and the assigned director was Jay Roach, then a hot property in the wake of Austin Powers (1997). Once again, Adams found himself living in the States, working on new drafts of the screenplay. There was still hurdles to face, but it looked like there might be light at the end of the tunnel. Then, in May 2001, Adams died without warning in his local gym. Understandably, the project went back into stasis.

Now, at long last, the film’s made and arriving in cinemas. Many have remarked how poignant it is that Adams never lived to see this come to pass. Adams’ screenplay has been polished up by Karey Kirkpatrick, writer of Chicken Run (2000). Jay Roach takes a producer’s credit, but has stepped aside for gifted British music video team Hammer and Tongs (director Garth Jennings and producer Nick Goldsmith). The jury’s still out on the end result. Hitchhiker fans who’ve sought out early screenings are divided about it. Leading Adams expert MJ Simpson ran a detailed, critical review on his long-standing Planet Magrathea website, only to close the website days later in response to flak his opinions drew on internet forums. Indeed, he’s announced that, "as of now I will never write another word, in print or online, about Douglas Adams or The Hitchhiker’s Guide to the Galaxy."

Perhaps inevitably, after its elephantine gestation, the film’s an unsatisfying piece, with appealing moments marbled into often laboured material. Certainly, those wary studio bosses were trying to tell Adams something: Hitchhiker’s really isn’t ideal film material. The earlier incarnations were freewheeling and eccentric, unencumbered by the need to bolt a solid structure to the tale. Here, the usual Hollywood trappings – a quest littered with obstacles, recurring antagonists and even a romance – prevent proceedings getting too unruly, but that misses the point that, in Hitchhiker’s, unpredictability has always been half the fun (nor does the process make the tale any less incoherent at times). Adams’ voice is so very distinctive, a unique blend of wit, philosophy and melancholy, that it’s difficult to do justice to, and there’s no denying that some blanding-out had occurred here (several of the key one-liners, especially from the Guide ‘entries’, have been shaved down to lose the specific references that made them so memorable in the first place).

It’s far from all bad, though. The cast, a curious hotch-potch at first glance, are talented and engaging, and certainly appear to ‘get’ the material. Freeman does well with the thankless role of Arthur Dent, and Mos Def makes for a memorable Ford Prefect (sadly Rockwell, usually so watchable, comes across slightly half-hearted). The design, too, is inspired and entirely suited. Perhaps, after all, the whole enterprise is just fundamentally misguided, but we’re left with a patchy piece that still manages to be an entertaining, and even touching, sort of mess. As to whether it was worth the wait, and does justice to the finest flights of its creator, we’re still waiting for the ultimate answer.