Cloud Atlas: I feel like some of the stories worked a lot better than others. In particular, the 'first' and the 'last' stories (I say those in quotation marks due to the book's fluid relationship with time) were the weakest of the lot. Indeed, as it got further into the future, I think it got better. I really liked the changing styles of prose as well as the really different characters that ended up populating the book. I have absolutely no idea how it's going to work as a film adaptation coming out this year (that was actually the main reason I bought the book), but it should be interesting, in any event. Whether it's an interesting masterpiece or an interesting trainwreck will be determined in due course!
The Magicians: It was sold to me as an adult version of Harry Potter, and while that's a slightly reductive reading, it does have a little bit of truth in it. Having said that, it's much less fantastical than it appears. Indeed, it's much more about the human and emotional connections made by the characters as opposed to the purely magical one. It's not a perfect book by any means (there are some big structural problems that I have with it) but I'd still recommend it.
I don't think the first three albums sold well enough in the US for the label to branch out internationally.... at least that's my rhetorical answer to your rhetorical question. Hence this was the gateway album.