It took me a while to crystallize my opinion on this one, but now I have it. First of all, I was expecting to read about a better detailed apocalyptic world, with a stronger scent of death. But I guess a virus does not have any smell at all, to satisfy my terror thirst with it. Fortunately, I found enough terror for my taste in Dr.Nichols' decisions and between the prison's walls.
Second thing, the novella is very to the point and, at the same time, the characters are very well shaped. Such a rare combination!
Third thing, I had a great time reading Human Instincts as I was fully connected to the story line, eager to find out what will happen next.