First off I have to say I agree with Manny's review. I really didn't like the business with Fermat's last theorem. I also thought the business with being basically perfect at chess was lame too. Lastly I thought the beginning was slow. I almost abandoned reading this one just because I wasn't really feeling it.
On the other hand, I will say that I thought the writing about the sex trade was interesting, and I thought the basic idea that they were going to do an expose about it was cool. I was a little disappointed that the solution was pretty tangentially related to this general discussion. I mean it's true that in some sense it is the cause of the two journalist's deaths, but on the other hand the whole business with Lisbeth's father and his history didn't have much to do with the ideas discussed by those journalists. It just happened that the sex trade was the connection.
Like Manny, I also found it to be a page turner once I got past the dumb stuff at the beginning about the Caribbean and her supposedly magical mathematical power. I definitely have a weak spot for adventure thriller type book even when I find the writing weak or silly.
I also learned a little about the difference between the book and the movie. My wife had watched the two movies and liked them, so I decided to read the books. About half way through this book I made a seemingly innocuous comment about Lisbeth being wanted for murder, assuming it would be perfectly clear what I meant. I won't say I completely dismiss that my wife may have been silly to say so but she said something about Lisbeth being wanted for the death of her father. Apparently this is something that is revealed even in the first movie, and therefore seemed to be a reasonable to assume I knew about. As it turns out though, all of the business with Lisbeth's father is left to the like the last 1/3 to 1/4 of the second book. It wasn't a big spoiler or anything but it did lessen some of the surprise when the big shoe is dropped about this stuff.
Anyway, recommend if you liked the first book but be warned there definitely some things to not like about this one. I will read the third one.