The most surprising thing about Michael Bay’s much-anticipated, blockbuster-bound “Transformers” is how “funny” the movie is. I don’t mean funny in an unintentional, “Pearl Harbor” kind of way: For more than two-thirds of its 144-minute running time, “Transformers” is essentially a comedy, something neither the film’s awesome trailers, nor Bay’s track record, ever hinted at.

The emphasis on humor, which is engrained in the script by Alex Kurtzman and Roberto Orci, then amplified by Bay’s uncharacteristically restrained direction and a cast of game actors, was a stroke of genius.

Humor is the key, really, to get viewers unfamiliar with the “Transformers” universe to buy into the premise without diluting or altering it – and risk invoking the wrath of the legions of fans (who, judging by the middle-aged guy who sat behind me at a preview screening, talking to the images on the screen as if they could hear him, are scarily devoted).

So even though “Transformers” is a movie in which giant talking robots with names like Optimus Prime and Devastator turn into Camaros, wrestle and punch each other and fight over a glowing cube that holds some kind of unimaginable power, there wasn’t a moment in it when I felt my eyes starting to roll.

Bay paces the movie shrewdly, waiting more than an hour before plunging all-out into scenes in which characters say things like “You hold the key to Earth’s survival!” By then, the film has cannily engrossed us in the archetypal travails of Sam Witwicky (Shia LaBeouf), a suburban teenager dealing with the usual issues of taking care of his first car, winning over the prettiest girl in school (Megan Fox) and keeping his meddling, albeit well-meaning, parents at bay.

LaBeouf, who is just as effortlessly charismatic and likable here as he was in the sleeper hit “Disturbia,” manages to give this special-effects enterprise a flesh-and-blood center. Even in the gargantuan, eye-popping action sequences, which contain some of the most seamless special-effects work ever put on film, Bay wisely keeps his emphasis on the puny humans’ perspective (a lot of the robots’ battles are shot from the point of view of bystanders on the ground or trapped inside their cars).

For much of the film, Bay even keeps his own worst habits in check, sometimes even holding onto shots for more than 30 seconds at a time (it’s as if he finally got around to reading some of his own reviews). In its climactic 20 minutes, “Transformers” finally becomes an all-out Michael Bay movie, with explosions and destruction whizzing by so quickly on the screen you can barely register it all. When the film is over, you’re not exactly sad to see it go (judging by the clunky abruptness of the last few minutes, even the filmmakers seem exhausted).

But by then, “Transformers” has won you over with bits like one in which Sam tries to keep his parents from noticing their front lawn happens to be full of metallic, skyscraper-sized extra-terrestrials who urgently need Sam to find the pair of glasses he’s hawking on eBay. The last thing anyone expected to find in a Michael Bay movie about warring heavy metal from outer space was whimsy.