I'm not sure what to say about this - I can see that it was an important book -- there are moments of lyrical beauty in it - But it is very hard to adjudge a book written in Japanese when read by an English only speaker.... On the other hand, the angst of the writer and the character -- Dazai himself committed suicide -- is.... it is no longer a very revolutionary act. Death is not a very revolutionary act. It is clinical... and while it may have shocked the bourgeois sentiments of the 19th century, the 20th century has shown that life, and living -- are, indeed, the revolutionary acts. Even if they ultimately prove impossible to sustain.
Of course, this is the problem with a lot (not all, but still a lot...) of the modernist literature I am reading -- a certain moral puerility.
I think the painting/art of modernism has, over all, held up better - though some of that too will not last. (I'm thinking mainly of kitsch -- and its descendants). In philosophy, almost nothing will likely last of the past 65 years, apart from Quine -- and possibly nothing from the last 100 years --
Though such sweeping statements will always prove false, I guess....
And I haven't read much in epistemology.
The breakthroughs in science will last... obviously. That, too, is a genre.