I don't know much about Shintoism besides very basic knowledge (and the fact that it could, and indeed was, used for extremism, ie WWII)
Most Japanese people don't know much about Shintoism. That's perhaps the beauty of it.
From complete ignorance it strikes me as being about nature and continuity. This of course could be harnessed by nutters, but nutters will harness anything that suits them.
I like Shinto because when I look out over the roofs of my dismal Osaka suburb, the only fully-grown trees I see are those in the local shrine. Only the Shinto let trees grow. (And me of course, but my trees only went in two years ago.)