Buddism is strong in abiding to cultural norms and bettering one self ( without the guilt trip, it is simply something one does for oneself ) while shintoism is very animistic.

(as faar i understand and say here in a very condensed way, in detail things are much more complicated offcourse)

But i think with the two together you get an mix that in average has better results compared to the monotheistic religions.

Not perfect, there was WW2 and so on, but for my opinion that was more an political thing, not religious motivated.

So...

If everything you do falls back onto yourself not because an god punishes you but simply because your action have consequences (buddism) and everything has an spiritual worth (shintuism) i think you have an mixture that works out better than the western desert religions.

For my feeling Japan has about the same idea as Iceland, people there asked who they belief in answered in the majority "Myself"