I don't know. With the cognitive relativism of our times, we want to make sure each civilisation, and each of its ages, are "equal". They certainly can be equally interesting for studies, but if we take a simple way to measure its effect on the human race by checking out how many books that are still read today have been written during these periods, you'll see that ancient Greece and Rome (and ancient China, and French enligthment) have been periods of great fertility, while for the normally educated man it is hard to find more than 2 or 3 books from the Middle Age that are still read and having influence nowadays.
So, at least following a few similar criteria, the Dark Ages were "dark". And it is not very surprising: when all the intelligensia spend almost all its brain power in obscure religious debates, you get very few results.