It's the age of reason
This is the classic claim for the eighteenth century, and the one that sticks. Generally, this has been seen as a good thing: Enlightenment thinkers aren't interested in faith or authority, they like to think about stuff. However, this isn't as simple as it seems. The ambition to apply reason to ideas means that there was plenty of argument, and a fundamental belief - that reason is the best thing ever - doesn't receive that much critique. 'Reasonable' can end up being like 'Christian', a word that isn't always used to mean the same thing.
They liked a bit of science
In the previous century, the scientific method had caused a revolution in the way that the Universe was being investigated. This encouraged the Enlightenment to apply a more scientific approach to sociology, frequently invoking science to justify their descriptions of human behaviour.
They invented branding
Although the French philosophes did hang out together, Enlightenment was a buzzword, and writers would slip it into conversation to prove that they were in the gang. This did mean it was easy enough for its enemies to point out their opposition, but it also meant that the wider movement got more hits than individual thinkers.
It was cosmopolitan
Being a cross-European business, there was less of the nationalism and more of the hands across borders - they were even pretty positive about African and especially Chinese culture. This respect for different societies - despite the odd racist freak-out - made the Enlightenment one of the first movements to have an inclusive philosophy (although Christianity, The Roman Empire and Islam might all dispute this, since they had Universal aims too).
It was about growing up
Kant said that it was about casting off the oppression of authority, of maturing. The rejection of tradition and religion was an attempt to make humans act like adults, and not cower in fear at a set of rules made up by a father-figure (like God or the King, or Aristotle)