Religious revivals seem to have short  life spans.  This includes bad ones.  Sometime it is just that people get swept up in some spirit. Sometimes it is pure Sitra Achra Dark Side revivals.
But sometimes even from the Bright Side they putter out.  Sometimes it is just purely human potential for delusions with a little help from the Dark Side. Sometimes it is from the Realm of Holiness, but still has some kind of time limit.
It is hard to judge what kind of thing was Flatbush, NY. To me it seemed very much like a religious revival from the Bright Side. It seems to be no accident that three of the greatest yeshivas in the world are there, and there was an amazing spirit of Torah.  Even when the revival aspect is over, it still is clear that the level of learning in these places is far beyond any yeshivas anywhere else with the exception of Ponovitch in Bnei Brak.
So what is the meaning of this? Is it just the moving of the Spirit of God on the face of the waters? Is it like predicting where the wind will blow?
There was an academic book on the experience of the אור אין סוף (Divine Light) that I heard about, but did not see. William James and Dr. Kelley Ross have dealt in thorough way about religious experience (from the Kantian perspective). But what about the positive side of revivals? The Musar Movement, the NY Yeshiva world from 1950 -1990? What is one to make of it?

Or rather I mean to ask a practical question. How to avoid the bad ones? How to tell if one is good? I got some good insight into this from Dr Michael Huemer's essays about objective morality and Dr, Kelley Ross and also Steven Dutch as I mentioned in this blog a few years ago when I was involved in reading their works. In the meantime my philosophical studies went on from Kant and to Hegel. At this point in life I am more in the ''after the revival'' mode even a good and great one like the Yeshiva World, how to get on with simply living according to God's will.
The yeshiva world itself in Israel seems to be mainly about money. I was very disappointed in what I saw in Jerusalem. Or, rather I was horrified.
It is like a condemned building. The best thing is the leave it before it falls down. The best idea is to learn at home, or find place of Torah that is real and has the real spirit of Torah.
People that are totally against Isaac Luria might not appreciate my point of view, but my basic feeling about  the kinds of phenomenon discussed here really comes from my reading the Eitz Chaim of the Ari. I dare not mention the Ari much because if anyone is misused, it is him. Still I think I gained a lot by reading him.   In fact being part of the religious revival that was the NY Yeshiva scene and then learning the Ari and then coming to Israel I believe kind of lit a fuse in me.