Picture the scene: Johnny Depp is living with Hunter S Thompson in the latter's house in Woody Creek, Colorado. The celebrated actor is preparing to play Thompson in Fear and Loathing in Las Vegas and is boarding with the anti-hero journalist in order to get a handle on his character.

One day, with a bellyful of bourbon, Depp wanders around the basement and finds an old manuscript. It turns to be a discarded semi-autobiographical novel written by Thompson. Depp reads and loves the story and forces his friend to get it published – which Thompson does.

The book is a success and Depp then sets out on a personal project to get the novel made into a movie. The Rum Diary is that book and that film.

The film's plot tells the tale of Paul Kemp, a down-on-his-luck, failing novelist, who has fled New York City for Puerto Rico in the late 1950s.

There, Kemp picks up work at the San Juan Star newspaper and attempts to work out where he is headed in life, clearly jaded from several knock-backs for his novels.

The newspaper turns out to be a halfway house for alcoholics, drunks, narcotics aficionados and almost coincidentally, writers. The audience is brought on Kemp's journey as he tries to balance being a journalist in the Caribbean with drinking rum; taking drugs consumed through the eyes; attempting to claim a slice of a fortune through a property venture; and falling in love with his friend's sultry girlfriend, played with a Marilyn Monroesque femininity by Amber Heard.

As with so many adaptations, the film deviates from the book in many respects. Bibliophiles who hoped for a page-by-page retelling will be disappointed, as the novel is not lovingly recreated line by rum-inspired line. Not even close.

Instead of a completely faithful adaptation, what the audience gets is an artistic ménage à trois between the original plot, director Bruce Robinson's reimagining for the screen and Depp's portrayal of the iconic Thompson.

Robinson was coaxed out of semi-retirement by Depp to make the film and many thought it a dream-team combination. The director's Withnail and I is a classic and the plot of The Rum Diary is tailor-made for the director's alcohol-stained depictions of life. He gets excellent performances from the cast - especially Heard, Aaron Eckhart and Michael Rispoli as Kemp's confidant and colleague Sala. The choice of Dariusz Wolski as cinematographer is a well-made one, with the Pole depicting Puerto Rico with beautifully simple shots and shades of ochre throughout.

Fans of Robinson's work will be interested to know that some of the lines in this film are lines that failed to make it into Withnail and I – which gives you a flavour of the themes.

The main problem with the film is that the plot is quite simply not as good as the original novel's. One of the novel's central characters, called Yeoman, is removed and combined with the Sanderson (Eckhart) character in the film – this is to the detriment of the story. Some of the jokes fall flat, while others hit the mark and the denouement is not played out well.

That said, the original novel is brilliantly rambling and the film follows suit with a series of drunken escapades, which - at times - light up the screen.

Fans of Gonzo journalism will be delighted to see a depiction of the godfather of the genre before he made it big in the United States.

The atavistic depictions of drinking and debauchery - which are Thompson's trademarks - are present on screen; while the film also depicts a different time in journalism: a time when a self-respecting writer was armed with a typewriter, cigarettes and plenty of booze.

The Rum Diary forms a trilogy of sorts with Art Linson's Where the Buffalo Roam (1980) and Terry Gilliam's Fear and Loathing in Las Vegas (1998).

The previous two films concentrate on Thompson at the height of his career in the '70s – a man who was by then world famous for his writing. The Rum Diary focuses on Thompson as a struggling journalist prior to any acclaim, and in this sense it serves as a prequel.

There have been articles stating that this film has been a box-office flop compared to some of Depp's other recent films – the hideously boring and repetitive Pirates of the Caribbean franchise for example. The Rum Diary film cost $45m to make and only took in $5m when opening in the US. But The Rum Diary is an indie flick at heart that was never going to be number one in the box office for weeks on end.

It was a personal project for the filmmakers. It's a project that was made in the hope of portraying a story of depravity, decadence and desperation on an idyllic Caribbean outpost before the tourist boom in the region.

Thompson said he wrote the book in the hope of penning the Great American novel, but instead wrote the Great Puerto Rican novel. This is a valiant attempt to make the Great Puerto Rican film; whether it achieves that aim is debatable, but it's quite a ride.

Silver-screen tales of degradation are not for everyone, but those who do like them will enjoy this escapade.

The cultural subtext of the white man subduing the native population is present; however, it is more of a setting than a central subject. The main thrust of the film is a glimpse into the '60s, through the eyes of drinkers, writers and lovers.

Tadhg Peavoy