well, there are many ways to be one sided...
the book relies heavily on "holy blood, holy grail", which was a major hit some time ago. holy blood is a very thorough research, which is still debated today, although the dossiers secrets on which it is based are now widely considered to be a hoax (still debated though). all of the real life symbols in browns book are authentic (can be verified), as well as its claims about christian history (although in that it only touches the tip of the iceberg of what any well educated christian scholar already knows). to add to the fun, the book is riddled with allusions to other sources (holy blood, currently living people, literature and christian history as well as many more). the fact people are disappointed by it being fiction is the best testimony to how good the book is. wouldn't you have liked it if it was all real?
anyway, it should serve as a portal, or an eye opener. start reading about christian history (holy blood, holy grail. fell victim to a hoax, but still fascinating), templars, excavations under the dome of the rock (even in modern day by some chief rabbis...) and of course the illuminati and free masonry, which is still very alive and kicking (easier to see it outside israel, but still...)
and about the dark wave of superstition washing over us, this book does not promote paganism, it just tells the truth about the pagan residue in christian dogma. it is very interesting the book (which challanges christian belief), became such a major hit in the US, which is very religious.