"Cloud Atlas" is based on David Mitchell's 2004 novel of the same name, which was widely considered unfilmable -- even after "The Matrix" directors Lana and Andy Wachowski and "Run Lola Run" director Tom Tykwer started working on it. It has received mixed reactions from critics, many of whom are still scratching their heads, trying to figure out what the nearly three-hour-long film meant.

But the actors involved didn't have to think twice about signing on. That's even though they all had to play multiple roles -- up to six apiece -- in the film that spans five centuries, sometimes playing characters of a different race and sex.

"Take the word 'fun' and infuse it with as much importance and delight as possible," Tom Hanks, who appears in all six loosely connected stories, told a small group of reporters in Beverly Hills, Calif. "Because quite frankly, eating pizza's fun, but doing this, I think for everybody, was part of being in the greatest repertory theater company imaginable."

Halle Berry, sitting beside him, plays Hanks' love interest in one story -- and very different characters in the other five. "Nobody would have ever picked me to play a Jewish-German woman or an Asian man. I mean, ever," she said. "So there was a knowingness when this was all happening that this was pretty special, and as artists, we should soak in every moment."

Susan Sarandon agreed to join the film before she'd even read the script. "I just knew something special was going on," she said. "Tom Hanks is iconic." She added, somewhat surprisingly, "Some of us consider ourselves more character actor-y."

Hugo Weaving, who plays villains in all six plotlines, found portraying so many people in one film less difficult than you might imagine. "It's liberating in a way because you're not focused or precious."

James D'Arcy was just as enthusiastic about playing major characters in some stories, and barely speaking in others. "It was almost more fun to play the small roles." Fellow Englishman Ben Whishaw, talking to reporters alongside him, agreed. "I want to play an extra again," he laughed.

"Did you find yourself acting like an extra?" D'Arcy asked him, joking that he kept wondering, when playing those small parts, "When's lunch?" Whishaw mused about playing a woman, "I'd like to have another go at that, actually."

"Cloud Atlas" was a first, then, for many actors -- and in an entirely different way for Jim Sturgess. "I'd never been to the future," said the actor. How does one prepare to play a character living centuries-hence? His co-star, Korean actress Doona Bae, found a novel way to do it. "I went to Berlin all on my own," she reported. No managers, no assistants. It helped her to get into character as a replicant living a miserable future. She felt she had "to empty myself, empty my heart."