I really liked this one, largely because of the structure. I'm a big fan of stories that drop you in at the middle (Or in this case, basically the end) and work backwards to fill you in and I thought this did a really good job of it. Similarly, the way that Randolph's background was sketched out was more than enough to cast a shadow of doubt over his actions, making the end all the more effective.
Finally, the eventual payoff whilst I suspect a little too pat for some listeners, fitted very well with what had gone before. I liked the fact that there was no explanation for what the sickness was, I liked the fact that we were left with questions and I particularly liked the way Randolph's physical and mental disintegration was portrayed. Not just straight horror, but very good straight horror this is one of my favourite pseudopod stories so far.