Don't watch if you haven't read the book!

Usually when I watch a movie and don't understand all that's going on I will read the plot summary in IMDB or Wikipedia and come to an understanding. Not so with this movie. There's just too many characters and too many plot threads for a movie or even a short summation. Only in a book-length form can such a complex series of events be adequately presented. The movie intentionally leaves out details (e.g., why did they not show who was making out with Smiley's wife? Was it disguised in the book too?), with the presumed motive of increasing suspense, and to some extent this is the M.O. of spy novels themselves; however they just couldn't make it work in a 110' film.