I prefer to read original language rather than translation, am suspicious of sudden hits, rarely read crime novels, and virtually never start a series partway through. In this case, however, I needed some thick travel books for a long layover, and I took what was available at home - the final two books of the Girl Who/Millennium series. I'm clearly one of the last to read these.
I have seen the Swedish film of The Girl With the Dragon Tattoo, so I had some of the book 1 background. And Larsson does a good job of providing necessary background in an unobtrusive way. Girl who Played with Fire was (to me) a pleasant surprise. Reg Keeland's translation of Stieg Larsson's prose is extremely readable. The style is short and to the point, and a nice carrier for Larsson's detailed but not florid descriptions. There's a wealth of information, but it's presented in a nicely organized, very journalistic fashion.
The plot revolves around journalist Holmkvist's efforts to help colleagues investigate sex trafficking in Sweden. Trafficking in persons is a grotesque crime that few people seem to think about, and I appreciate Larsson's effort to bring it a little more into the spotlight. While his matter of fact descriptions of how it works were grisly, the reality is much worse.
As things go on, the web of people involved grows and grows, eventually involving (of course) Lisbeth. Despite some descent into Swedish political history, and a large cast of characters, the book was clear and easy to read throughout. Even though it ends without a clear final solution, the end is satisfying.
All in all, as you've no dount heard elsewhere, Girl who Played with Fire is a well-written, easy reading, massive book, and worth a look whether you like crime fiction or not.