First, one could say that the term "Dark Ages" is one applied to the time period from the Renaissance to the medieval period. Most contemporary scholars see the term as misleading at best. Instead, most scholars prefer a value neutral term, such as "Middle Ages" or "medieval period."
The period between the fall of Rome and the Renaissance was highly transformative: it involved a significant redistribution of power. Although the western, Latin-speaking Roman empire fell, the Greek-speaking east, otherwise known as the Byzantine Empire, flourished, creating great works of art, literature, architecture, philosophy, and theology. As a result of the "Great Schism" and the increasing lack of communication between the two regions, there was increased separation between western Europe and eastern Europe.
Next, the Middle Ages were the period which saw the rise of Islam and the broad spread of Islamic civilization across the southern Mediterranean into Spain. It was also a great period of flourishing of Islamic science, medicine, and mathematics. In Spain and the eastern Mediterranean, Islamic rulers came into contact and fought with Christians, having fruitful cultural exchanges as well as less productive violent interactions.
In western Europe, one can see the development of major new centers of power in the north. There is also a language shift; Latin evolves into the Romance languages. Feudalism also became a major economic system.