It's hard to describe the effect the latest Hasbro Toys inspired 3D saga, Transformers: Dark of the Moon, has on the audience.

The overwhelming sci-fi action spectacle is a merciless sensorial assault that leaves you with something akin to post-traumatic stress disorder.

The third entry in brainless-blockbuster auteur Michael Bay's saga, Moon brings to a head the war between two alien mechanical beings, the Decepticons ("who dreamed of tyranny," says the voice-over) and the Autobots ("who fought for freedom").

In the middle stand the Autobot's allies, the human race, which is led - in spirit, if not in fact - by hyperactive manchild Sam Witwicky (Shia LaBeouf) and his girlfriend Carly, played by an exquisite, if virtually somnolent, Rosie Huntington-Whiteley.

Clocking at a monstrous 154 minutes, Moon is a stunning, unremitting phantasmagoria of car chases, metal-crunching crashes, jet fuel-fueled explosions, machinegun fire, car chases, crashes, explosions, gun fire, car chases . . .

You get the picture.

The pic opens with a montage of cleverly altered archival footage that tells a reimagined history of NASA's Apollo program. We learn that in 1962, President John F. Kennedy launched the Apollo program to study a UFO which had crashed on the dark side of the moon.

The craft is piloted by the Autobot leader Optimus Prime's mentor, Sentinel Prime (a particularly soft-spoken, velvety voiced Leonard Nimoy).

Sentinel Prime has a piece of super-duper high tech which both sides in the war are desperate to acquire. So they duke it out.

There are some betrayals, sad farewells and deaths. But ultimately, the will for freedom, truth, goodness and beauty triumphs.

The final battle unfolds in a frenetic, impossibly complex one-hour set piece of flying fireballs, mangled metal and severed human limbs that is mind-boggling for its sheer audacity and length.

It's a cinematic purgatory you keep praying will end. It doesn't! Bay's idea of a successful film is to beat the audience into submission.

The director doesn't lack subtlety, he doesn't know what the word means.

Yet as bad as the action sequences are, Bay fails spectacularly when he goes for pathos

We're treated to inumerable languid sequences of bullet-riddled American flags waving in sorrowful slo-mo as the camera pans across dead soldiers. The music shifts from its default setting - swelling patritotic heights of warfare ecstasy - to rock ballads by sensitive singer-songwriters (kid you not).

If we feel anything for Bay's soulless characters, it's for the 'bots. His camera barely conveys a shrug when the Decepticons massacre women and children, while he expertly manipulates us to tear up whenever the 'bots are hurt.

Always secondary in a Bay film, the actors do manage to do their jobs adequately.

LaBeouf, a graduate of the ants-in-your-pants school of acting, plays Witwicky as if he had a ferocious case of attention deficit disorder. After two films, his fidgeting isn't cute anymore.

He's ably assisted by franchise regulars Josh Duhamel, Tyrese Gibson and John Turturro. New additions Frances McDormand, Patrick Dempsey and John Malkovich add some spice to the mix.

Huntington-Whiteley's role is to make teen fans drool. So she purses her lips a lot. (We're way beyond sexism here.)

Megan Fox, who did the thankless, demeaning Hot Babe job in the first two Transformer films, at least brought some personality and humor to the role.

Moon seems to have little but contempt for viewers, bullying us at every turn. And it has a cynical view of the world, endorsing, as it does, war for its own sake.

At one point, Bay has Optimus Prime declare, We'll kill them all.

You may not know it at first, but he's referring to the audience.