What was life in Western Europe (outside Italy) like before the Romans imposed civilization? Celts and Germans and other assorted barbarians who scratched a meager living in the fields. Most people, unless there were mass migrations, were tied to the immediate lands and lorded over by some petty chieftain sitting in a nearby hillfort. Wealth was not so much created as it was stolen from one's immediate neighbors; the petty chieftains chief occupations were to wage war on each other and plunder each other's meager wealth. Where literacy existed, it was usually confined to a few religious specialists, and those religious specialists exercised undue control over society at large.
Seems to me the Romans brought 4 or 5 centuries of civilization to the West; when central Roman power collapsed those societies simply reverted to more or less what they had been before the Pax Romana.
Of course, some things had changed forever, outside of Britain at least. Latin or some version of it replaced the local languages. Roman Catholicism replaced (or rather absorbed) local religion. There was still some memory of Roman law. All these things would endure through the Dark Ages and make Western Europe what it is today.
In any event, only the Western portion of Europe was dark. The East was still quite cultured and wealthy, though sadly it poured its energies into ridiculous religious disputes. When the East fell, its scholars fled to Italy, helping give birth to the Renaissance.