Have you read Vinson Synon's book on the history of Pentecostalism? I understand he died only this year? I read two of his books, and would heartily recommend them.
As I recall, he told the story of Seymore, but the phenomena was hardly pure!
It included many false displays more on the order of self-aggrandizement, or even the occult, at times. That couldn't be helped, it seems. The cat got out of the bag, and there were bound to be distractions, and people filled with themselves, wanting to be exhibitionistic.
But overall, I do believe it was an endtimes outpouring of the Spirit, leading a world-wide renewal of Christian Civilization. It is a 3rd major movement in Western history, along with Catholicism and Protestantism. I can't conceive of a solid work of God without the manifestation of signs and wonders, by the power of the Holy Spirit.
I think all major moves of God have had some of this, however. What I like about Pentecostalism is its emphasis on demonstrating spiritual gifts by all, and not just by the leadership. For me, the important thing is to extend outwards, towards developing new leadership, and cooperation among all, rather than just turning inwardly and exclusively, which is what I believe destroys moves of God.