Forget movie critics. There may be no more unforgiving, opinionated and passionate film audience than the one in cyberspace – the fans, the obsessives and the self-proclaimed geeks who hang out in Internet discussion forums commenting on every casting decision, every script rewrite and every shred of pre-release advertising material for movies that haven’t even been made yet.

And “X-Men: The Last Stand” – the third installment in the acclaimed mutant-superhero franchise – has come under closer scrutiny than most. As anyone familiar with the comic books will happily tell you, this is NOT just another “X-Men” movie. This is the story of the resuscitation of telepath Jean Grey (played by Famke Janssen), who died at the end of the second “X-Men” film, and her transformation into Dark Phoenix, a mutant so powerful she is capable of destroying entire planets.

Originally published in the 1980s, the Dark Phoenix saga is one of the most revered story arcs in comic book history – a complex, operatic and tragic tale that had long-reaching repercussions in the X-Men universe. To say that the anticipation for the movie is high does not begin to describe it.

But so is the skepticism. When Bryan Singer, who directed the first two “X-Men” films, announced he was abandoning the franchise to make “Superman Returns,” he was replaced by Matthew Vaughn, a veteran producer who had directed only one movie, the British gangster thriller “Layer Cake.”

Then Vaughn, too, left the film – only nine weeks before shooting was scheduled to begin – and was replaced by Brett Ratner, whose resume (“Rush Hour,” “Red Dragon,” “Family Man,” “After the Sunset”) apparently did not meet the standards of the “X-Men” fan base.

Brett Ratner, left, reviews a scene with actor Patrick Stewart on the set of X-Men:

One typical posting reacting to the Ratner hire on aintitcoolnews.com: “The good news is, at least after ‘X3’ we won’t have to worry about anyone ever desecrating the X-Men again, because this can only be a bullet to the head of the entire concept of an X-Men movie.”

Ratner (who ironically was scheduled to direct “Superman Returns” before Singer signed on), knows all about the online vitriol leveled at him.

“And so I purposely didn’t read that stuff when I was making the movie, because it would have messed with my head.”

Instead, Ratner, 37, forged ahead with the biggest and most complicated film of his career. Although he had little hands-on experience with the extensive special-effects work an “X-Men” movie requires, Ratner says the six months he spent preparing “Superman Returns” taught him more than he realized.

Ratner, who admits he never read the “X-Men” comics but was a fan of the TV cartoon series, says he knew better than to tinker with the tone Singer had set in the previous two films.

“I wasn’t trying to put my mark on the series. I wanted to make a movie like ‘The Return of the King’ and how that fits into the rest of ‘The Lord of the Rings.’ I’m trying to be part of a trilogy.”

Although “The Last Stand” introduces some new faces to the ever-growing mutant roster (including Kelsey Grammer as the furry blue Beast and Ben Foster as the winged Angel), the bulk of the film centers on veteran X-Men (Hugh Jackman’s Wolverine, Halle Berry’s Storm, Ian McKellen’s Magneto and Patrick Stewart’s Xavier), whose characters were already well established.

Ratner says he did ask for some structural changes to the script, written by Simon Kinberg and Zak Penn, such as moving a giant setpiece atop the Golden Gate Bridge from the middle of the film to the end, giving the story a more spectacular finale.

But Ratner says his main goal was to maintain the momentum of the series.

“When I started prepping the movie, I realized that I didn’t really know the comic,” he says “I knew the cartoon, which is similar. But Bryan’s interpretation of it was amazing. His casting choices, Magneto’s helmet, how he made everything work in the reality-based world … he’s a genius. I concentrated on how to deal with Dark Phoenix. She’s blowing up planets. How am I gonna make this work? I just took a cue from how Bryan made his choices with the other characters and how he brought them down to Earth.