This is another of the books that goes along with the Stargate SG-1 roleplaying game, but it is really worth getting just for the non-game informational aspects. The writers make up a lot of material as background information, and that is quite fascinating.
What is some of the most interesting material is where the writers establish a timeline of history, relating to evolution of humans to the evolution of Goa'uld, and how the Goa'uld eventually got mastery over the Earth and then lost it.
The book even goes into how the Jaffa came about, and also how the Tok'ra split off from the Goa'uld. In one section they even work in the legend of King Arthur, relating it to the Goa'uld.
The book also has a lot of game-related material in it, but the origins and background material of the Goa'uld and other players makes this book worth getting.