Did you find these obsessions to be more common than e.g. in the US or Europe? It seems we have a lot of people who are weirdly obsessive about their niche hobbies / interests as well...
From my few years of experience here in Tokyo, what I feel is that an obsession about something here (being an otaku) doesn't have a negative connotation in most cases, whereas in the US, being a "fanatic" is generally not usually a positive term.