The film is based off of the Don DeLillo novel of the same name, and follows 24 hours in the life of a newlywed billionaire, and sees him cheat on his wife, get stalked, and ultimately loses control over his fortune.  Just a day in the life of Robert Pattinson I guess.
Joking aside, the addition of Knightley, while coming at the expense of one of today’s most interesting actresses in Cotillard, is quite compelling.  I’m a relatively big fan of the actress, so while she may not be quite as gifted as Cotillard, you could do a whole lot worse.  Personally, this is still one of the most compelling films currently in the pipeline, so while it appears the entire cast is getting revamped, it doesn’t seem to be losing all that much steam.