I, too, have read this book. Amazon has been pushing it at me for some time, so eventually I decided to order it.
I am in two minds as to how to rate the book. The first two hundred or so pages were quite heavy going, with too much exposition and a frequently irrelevant depth of detail: for example, the description of Salander's employer, or the passage describing the destruction of her first laptop and her subsequent purchase. Characters were introduced who had no connection with the story and could easily have been edited out. Whilst I understand the necessity to describe what happened between Salander and her second guardian, in order to improve her characterisation, this section was too vivid, too long and too brutal (mirroring to a certain extent something which takes place towards the end of the book).
But after the two protagonists meet, sparks begin to fly and the pace hots up considerably. Once the major problem has been solved, the last hundred pages or so seem like an anti-climax, although actually this part is much more rewarding and could have been made into a novel by itself.
Reviewers on Amazon have mentioned unlikely coincidences, but almost all fiction depends on such devices. The skill of the author is measured in how believable he can make those coincidences, and I think that the late Steig Larsson managed quite well in that respect.