The Renaissance tended to portray itself as a period of enlightenment and movement away from the barbarism of the "dark ages", more properly termed the medieval period, preceding it. The reality is more complex, though.
First, in religion, the Renaissance was marked by the Reformation, which consisted of two different approaches to church reform. One resulted in Protestantism, which broke away from the authority of the Roman Catholic Church; the other—properly termed the counter-Reformation—attempted reform of abuses within the Church. The dark side of this reform was the ensuing period of devastating religious warfare that consumed Europe.
The Renaissance was a great era of exploration. Although this increased Europeans' knowledge and understanding of the world and led to many scientific discoveries, it had a dark side in the development of conquest, exploitation, and colonialism of peoples in Africa and the Americas.
The development of new technologies is often viewed as a positive element of this period, but this also included advanced weaponry, which allowed people to kill each other far more efficiently than they previously could. New technology also made many jobs obsolete, disrupting the lives of skilled craftspeople.