What is "natto"?
The traditional way of fermenting the soy beans was to wrap a few pounds of them in straw. Some yeasty microbe usually in that environment does the deed. I find some significant variation in the taste, some I cannot stand, some quite tasty. At worse (to my palate) it is sulphury and putrid; at best it is rich with a taste both "earthy and rustic" and refined. Perhaps a parallel to those who have not directly encountered it is some types of soft pungent cheeses.
A common way of eating it is for breakfast, as a topping on your bowl of rice. It can also be found wrapped up in a norimaki with the usual rice.
Once I participated (crew) in a TV show from Japan asking people on the street in the US if they would like to eat some. Everyone they encountered on that day wrinkled up their nose and declined. The Japanese were greatly entertained by that.
A good friend of mine in Japan goes through natto withdrawel if he goes to long without it. A lot of regional variations are found in Japan, most of the flavor differences attributed to the local fermentation variables. Interesting that you make the analogy to soft-ripend cheeses, he notes that he encounters an almost identical, negative reaction from Japanese to bleu cheeses he brings back as westerners have to natto. I have been presented with it a number of times and have not aculturated my palate enough to get past the smell (and I am pretty open to about anything!).