X-Men actor Hugh Jackman has told fans of the film not to expect a run-of-the mill sequel from the second instalment of the futuristic fantasy.
Jackman returns as Wolverine, the solitary fighting machine
Jackman, who reprises his role as the mutant Wolverine for X-Men 2, said the film was a much more intense experience.
"It is a darker film. It gives even sharper focus to the complexity of the characters and the world and its issues," said Jackman ahead of the world première in London on Thursday.
X-Men, based on the superpowered Mutant characters of the cult Marvel comics, was a huge box office hit in 2000.
The second film reunites all the original X-Men, as they battle to
overcome the human threat posed by former military leader William Stryker, played by Brian Cox.
X-Men was presented to me as something rather gritty and crucial
Stryker is bent on annihilating the already discriminated-against Mutants and begins an offensive on the X-Men mansion and school.
Among the returning cast members is Sir Ian McKellen, who plays the evil mutant Magneto, adversary of the X-Men Professor Charles Xavier, played by Patrick Stewart.
Sir Ian, who is also well-known for playing Gandalf in the Lord of the Rings series, said he always hoped there would be more X-Men films.
"I was very impressed that director Bryan Singer wanted to make a sequel, having had rather a triumph with the first. It felt like there was a job that was unfinished," said Sir Ian.
"Like us [the cast], he felt the first film had just been an introduction, only with this film can you lay out what X-Men really means."
In the movie, each X-Man has special powers. Wolverine is a solitary fighting machine with healing powers and retractable metal claws.
Magneto can control and manipulate metal. But beyond these abilities, each is also a thinking, feeling individual.
As a such, the mistrust with which they are treated by normal humans on Earth is not easily brushed off.
And, behind the fantasy and escapism of the special effects lies an enduring morality about our treatment of each other, added Sir Ian.
Sir Ian McKellen's character was locked up in the first film
"X-Men was presented to me as something rather gritty and crucial," he said.
"And I know from Marvel that X-Men is their favourite publication because it appeals to young gays and blacks and Jews.
"They all identify themselves as Mutants because of the way we treat them."
Also reunited in the film are Halle Berry as Storm, Famke Janssen as Jean, James Marsden as Cyclops, Anna Paquin as Rogue, Rebecca Romijn-Stamos as Mystique and Shawn Ashmore as Iceman.
But new to the cast is Alan Cumming as Nightcrawler, a character familiar to readers of the comics but new to the film franchise.
Cumming, a British actor who has found big success in the US, said the film's human message "spoke" to him and persuaded him to take the part.
However, nothing would prepare him for the tough time ahead, Cumming added.
Alan Cumming's character will be familiar to fans of the comics
Mutant Nightcrawler possesses incredible powers allowing him to leap through and off walls at supersonic speed.
He also stands out because of his impish appearance, with blue skin, tattoos, and a tail.
"I underestimated how physically gruelling it would be," said Cumming. "And I had to spend four hours in make-up every day and was constantly having it touched up."
Cumming was advised to train for Nightcrawler by going to the gym, which he willingly did to be able to do as many of his own stunts as possible.
"I wanted to show the stunt men I was not scared, I wanted them to be impressed but it was pretty scary," he said.
Nightcrawler's introduction was particularly welcome to actress Rebecca Romijn-Stamos, whose character Mystique can take on the appearance of anyone she wants.
Mystique is also heavily made-up and the actress was glad to find an ally in Cumming.
"You know what they say about misery loving company, so it was good to have another person to sympathise with," she said.
Rebecca Romijn-Stamos is unrecognisable as Mystique
"I had felt so alone in the first movie. But Alan and I were the freaks among freaks."
Like Cumming, Romijn-Stamos also had a lot to contend with physically.
She is virtually naked beneath the body paint and in one scene has to walk out, including without shoes, across a snowy wasteland.
It was difficult and pretty unpleasant at the time, said the actress, but seeing the completed movie made it worthwhile.
"It was so great, it was like giving birth - and I can't wait to do the next one," she added.
Her enthusiasm - if not the analogy - was repeated by the rest of cast, not least of all Sir Ian.
Asked about the X-Men's film future, he concluded with his own master plan.
"What I envisage is something more dramatic and expanding than just another X-Men 2 after this.
"The storylines in the comics have evolved and the principal characters have gone on to have their own comics, so why can't we all have our own films."
X-Men 2 opens in the UK on 1 May.