The Black Death was one of the most critical turning points in the development of western civilization. In fact, if you overlook the deaths of millions of people, it could be said that the plague was one of the best things to happen to medieval Europe. The drastic population reduction led to the breakdown of the moribund feudal system and the widespread disenchantment with the corrupt and ineffective church was one of the major factors in the Reformation. Europe's traumatic experience with the plague also led to the development of science and medicine after a long period of stagnation.
Europe before the plague was in a social, religious and political quagmire, its growth stunted, almost paralyzed, by its bankrupt institutions. If the Black Death had never happened, the West wouldn't have emerged from the so-called dark ages for centuries -- if it ever managed to emerge at all. Sometimes a system gets so screwed up that the only way to save it is to tear it down and start all over again. In many ways, the Black Death did exactly that and gave Europe a chance to develop into the modern world we see today. Whether that was a good thing or not is a matter of perspective, I guess. We can appreciate the way things worked out, but the people buried in the plague pits would probably disagree.