DEDICATED to the memory of its creator, Douglas Adams, who shares a screenwriting credit with Karey Kirkpatrick, The Hitchhiker's Guide To The Galaxy is an energetic tribute to the great man and his zany imagination.

Unfortunately, for all its visual invention and occasional strokes of genius, Garth Jennings' film is rather muddled and - fittingly perhaps - scatter-brained.

Many of Adams's flights of fantasy are crammed into the 108-minute intergalactic flight time but at the expense of coherence and fluidity.

Arthur Dent (Martin Freeman) makes a startling discovery: Planet Earth is about to be vaporised by the Vogons to make way for a hyperspace bypass.

Beaming onto a passing spacecraft with his best friend Ford Prefect (Mos Def), who turns out to be an alien in cognito, Arthur eventually finds himself in the company of the president of the galactic government, Zaphod Beeblebrox (Sam Rockwell), a paranoid android called Marvin (voiced by Alan Rickman), and the only other human survivor, Trillian (Zooey Deschanel).

Aboard Zaphod's state-of-the-art spaceship, the Heart of Gold, the hapless adventurers embark on a journey of a lifetime, encountering a menagerie of strange beings.

En route, Arthur discovers that a towel might just be the most useful item in the universe and that if he ever gets stuck, he can always refer to The Hitchhiker's Guide To The Galaxy (voiced by Stephen Fry).

The Hitchhiker's Guide To The Galaxy begins promisingly with a dolphin song and dance number that perfectly captures Adams's irreverent sense of humour.

Special effects are impressive throughout - The Guide is now a smart computer laptop complete with cutesy graphics and Fry's pitch perfect commentary - and there are some great set pieces like the surreal sight of a giant sperm whale (Bill Bailey) falling through the air to its doom.

Freeman exerts an undeniable charm and innocence as Arthur, who witnesses the destruction of his planet with the stare of a rabbit caught in the headlights.

Mos Def is also sporadically amusing as Ford Prefect, Deschanel makes something out of her nothing supporting role and Marvin is adorable.

Unfortunately, from the moment Rockwell gallops onto the screen, with the swagger and shiny couture of a faded rock star, the film never achieves light speed.

He wisecracks, rocks and rolls, jerking back his head to reveal a second face concealed in Zaphod's neck, but Rockwell appears to be acting in a vacuum, completely separated from the other performers.

Two heads are not, as the saying goes, better than one.