My verdict: This is a fascinating read and rife with interesting historical details. The science is clearly explained, though I can't be sure how accessible it is to someone who has little or no background in it. Sometimes Judson's inner poet sneaks out and his prose becomes quite remarkable. But it is usually pedestrian and sometimes jumbled—you can tell he's trying to squeeze in as many historical facts and biographical remarks as he can, and sometimes he doesn't seem to notice that his writing needed some smoothing out. But when he lets his pen run free, his writing really does sing. Sometimes Judson mentions things that have either slipped out of the 'mythology' of molecular biology or that never were part of it in the first place (e.g. inside jokes). These asides were often bewildering.
One other thought: I don't think it was Judson's intent, but Max Delbrück came across to me as something of a tragic figure. He was hugely influential in the history of molecular biology. His experiments with mutation in bacteriophage (which earned him a Nobel Prize) influenced Erwin Schrödinger. Schrödinger's book What Is Life? prompted a mass exodus of physicists into biology. These physicists were instrumental in developing molecular biology as a discipline and in discovering the structure of DNA, proteins, and the gene and especially how those structures contributed to function. Delbrück organized a group of scientists, informally known as the 'Phage Group', who made major advances in these areas. But Delbrück himself, it seems, got left behind. He was supportive, though skeptical, of the structure of DNA announced by Watson and Crick. But he rejected many other major advances that followed, including the discovery of lysogeny (mouse-over for definition) and messenger RNA. This made it seem to me that Delbrück was slowly marginalized because he couldn't keep up with the progress of the field.
 For example, at one point Judson mentions the Pardee, Jacob, and Monod experiment and that Monod had the thought that if the first letters of their last names were used to make a Hebrew word it could only be pronounced one way. Well, I haven't been able to find much. The Hebew word פִים pîm (the letter י can also be transcribed as j) occurs in 1 Sam. 13:21 and describes a polished stone that was used as a weight standard in ancient Israel (see here). I kind of suspect that's not the word Monod was thinking of. Perhaps he's simply referring to the fact that from then on the experiment was called the PaJaMo experiment. If not, then I have no idea what this passage is refering to.
A ribbon model of hemoglobin is by Benjah-bmm27, available at http://commons.wikimedia.org/wiki/File:Haemoglobin-3D-ribbons.png.