Not that I read many books by Dan Brown, ("Origin" being second after "Da Vinci code" that I read), "Origin", I should say, is a good one. Spain and its historical cites and state-of-the-art architecture are described in a beautiful language. Facts and mythology is captivating and as it was said in one of the previous reviews is a reason in itself to read the book.
Also I would agree that the Kirsch's discovery was not that satisfying I will say in defense of Brown that we should not expect a whole scientific theory or straightforward evidence of the beginning of life on Earth in a novel. Brown's knowledge of science is as broad as his knowledge of art and he did a great job at coming up with the idea.
Sometimes I felt a bit annoyed at the stretch of prelude before learning what the discovery actually was. Taking one star because of that. MIGHT BE A SPOILER: I would like to add that the plot was in some way similar to one from "Da Vinci Code" so it was not hard to guess who was giving the orders to murder, though a bit harder to guess why.
Beautiful description of locations, lots of interesting facts, theories and ideas to think over.