Rarely does one encounter a work as ambitious as Cloud Atlas. Not many works are willing to delve into many cultures and societies as much as this.
David Mitchell's novel is certainly a very ambitious piece of literature, that goes without saying. As stated above, you don't come across a piece of fiction that's this bold and daring. I don't know how long it took Mitchell to write Cloud Atlas, but his work just radiates on the page.
The adaptation by Andy and Lana Wachowski and Tom Tykwer is equally ambitious but something about it feels off. Indeed there is something fascinating about a small handful of actors taking on a range of accents, races and nationalities (and, for some, sexes) throughout the course of the film, but the slight political incorrectness of it might be why it also doesn't work entirely. Moving on, you can certainly feel elements of The Matrix and Run Lola Run throughout the film. (The 2321 and 1973 segments, respectively.)
Between the two, there's a fair share of similarities and differences. For starters, the visions Mitchell wrote were brought very much to life by the Wachowskis and Tykwer. However, said visions were altered by them as well. (Hey, if you're making a nearly three hour-long adaptation, you've gotta make sacrifices.) Still, they succeed in keeping the mystic aura of Mitchell's novel alive.
So which of the two is better? Well, some of the segments translated very well on the silver screen. However, the other segments flow better on the page than the screen. Both have their strengths and weaknesses, but only one can be deemed the victor of the two. (It's pretty clear, don't you think?)
What's worth checking out?: The book.