At 59 years of age, the best books in my life have been Lord Of The Rings, and Steig Larsson's Millennium Trilogy. Poles apart, but from a captivating 'must keep reading' angle, that's how it is.
Whilst reading the books, I smiled and doubted anyone could play Lisbeth Salander, so quirky was her character, and with such an odd and skinny body. But then we didn't know Sweden, much like they had Steig Larsson tucked up their sleeve, they also had Noomi Rapace - and the rest of the cast, of course.
Like the books, the movies are wonderful, dark timepieces set in a beautiful country, and despite much being omitted from the books to fit the 2 hour movie time-slot, the pace keeps you on the edge of your seat.
Read the books, watch the movies, you will not be let down by doing either and in any combination. The books have sold millions of copies for a very good reason, and the films will match them in the fullness of time. Top-Notch.