I am going to apologize super profusely and give you the chance to skip my comments now by saying that I have not read the book. Sorry!
However, when you were discussing the movie trailer - which I went ahead and watched also - everything about it reminded me pretty much of The Fountain - some elements of a great story kind of obscured by the gimmickry and "movie-ness" of the movie - super-budgeted crazy effects and colors, and even employing the same gimmick of literally using the same actor to portray connected characters across three stories - which, as you mentioned, feels almost cartoonish. The Fountain was not a horrendous movie by any means but if Cloud Atlas (film) falls into the same pitfalls I will be super bummed.
Also, I really should get around to reading it. Sorry again.