pschutz, do you have a chart to post? Because Neptune natally will show up by sign, house, and aspects, which will say something about how this person is hard-wired regarding Neptune.
Where Neptune hits the angles by transit or progression, and then either as a conjunction or opposition, obviously one's outward personality, career or public image, home life, and the committed relationship (if any) get affected.
The thing about Neptune, though, is that it doesn't deal in reality. Neptune gives us highs and lows, the beautiful illusions and bitter disillusionment, but it misses the reality in between.
This is why Neptune is good in the arts, where it augments Venus in creative realms. I personally think Neptune is the modern ruler of film (cinema.) Really what goes on in film-making are actors, a director, stage sets, make-up costumes, a sound crew, cameras, editing, and so on. But the illusion of reality (or an animated fantasy world) in the finished film. can feel very real.
I've also seen it prominent in the charts of scientists. I think the reason is that scientific research is essentially a quest into the unknown for new knowledge. If information were known, there would be no point in conducting research on it.
Neptune in hard aspect to the "me" points of the chart (sun, moon, ascendant) can bring about a crisis of self-confidence. Neptune tends to dissolve or erase what it touches. This loss of identity markers is really hard for some people.
Good activities? It depends upon the chart, but generally the fine and performing arts, as an aficionado, if not as an artist. Anyone can keep a journal or sketch book, where s/he can put Neptunian images to paper. Anything to do with the sea. Where Mars is involved, a sport like swimming or sailing. If the person is so inclined, spiritual pursuits. (Jupiter rules conventional religion: Neptune is more into mysticism.)
