As you might expect, The Cobra Event is not great literature, and it suffers from the flaws inherent in its factual origins. Too often, the action is slowed, or brought to a halt, by a didactic passage in which we learn more than we need to know about genetic engineering, or the structure of DNA. Preston has not yet learned that although factual knowledge is a help when laying out the story, the reader doesn't need to know even half of the detail. His idea of adding background colour is to describe the interior of a delicatessen where his protagonists eat lunch in the kind of detail usually reserved for travel guides (or maybe a Bill Bryson book). And there are no characters for whom the reader gives two hoots.
But the reader does, of course, care about the fate of humanity. The plot, such as it is, revolves around the race against time to catch the person responsible for releasing the plague, and to stop the spread of the disease. And the disease itself is a real humdinger, much worse than any flesh-eating bacteria.
This is where Preston really scores; the depth of his immersion in the background pays off. The physical effects of the virus are described in almost loving detail, and they are just close enough to the known effects of a real virus to make the idea of adapting it to attack humans more than merely plausible. You have a horrible feeling that maybe this part of the narrative is not fiction at all, but something Preston learned about from his work on The Hot Zone.
There is just enough pace to carry the excitement over the explanatory sections (which can be skipped) and send you hurtling on to find out not so much "who dunnit" but how they stop him. The effect is a bit like early Stephen King (the rats even make an appearance) or late Michael Crichton, but all the science is much truer to what is going on in labs than the science in Jurassic Park. Scientific non-fiction may have lost one of its stars, as the inevitable movie is already in the pipeline.