In my own early studies I learned that the transpersonal [generational] planets work in sequence to bring about evolution and change. Uranus moves in first to create instability and uncertainty, chaos and upsets. This serves to tweak the consciousness into realizing that change is an inevitable part of life. Neptune then moves in to clear the way for transcendence and higher understanding, by addressing our spiritual beliefs and visions. Pluto represents the fall from 'The Tower' in tarot; often bringing us to our knees, challenging us to rise like the Phoenix from the ashes and create new beginnings. Yes they certainly set the stage for our social and political backgrounds into which we are raised in.
On the personal level, Neptune, like all the planets, will reveal it's nature, not only through the sign it is in, but also by it's aspects, showing whether the energies will work for good, or ill in our lives. Already we have good insights into Neptune here [thanks to all who have posted]; I would also like to add a couple more keywords.
When it is positively aligned it relates to: imagination, trance states, [fantasy] , transcendence, intuition and spiritual attunement. It can also make us more in tune with Nature and all her beauty. Imagination is a strong facility when applied positively.
In it's negative forms though it sets us up for confusion, insecurity, naivete deceptions, betrayals, faith and trust issues and disappointments, typically by our own blind innocence.
It is also renowned for disguising our reality until we become awakened to what the true nature of reality is.