The word "Riesendurchfall" is really uncommon and it seems to be created by the author, perhaps to suggest an ambiguous interpretation.
"Riesen" means something like "big, giant".
"Durchfall" usually means "diarrhea", but it is also the nominalization of the verb "durchfallen" which means to fail in this context.
Therefore you get the interpretations
massive diarrhea (suggesting that the play was crap).
You write "It was a big success", but none of the above interpretations fits to this statement. I conjecture that the sentence was written by a detractor (... controversial due to its naturalistic style).
The premiere of the play was on October 20, 1889. In the linked article from Wikipedia one can read
Uraufführung, mit tumultartigen Reaktionen von Zuschauern, machte den Autor [Gerhart Hauptmann] bekannt.
This suggests that the play was met by boos from the audience; it was a big fail.
In contemporary German it usual to say that "Die Aufführung ist durchgefallen" or "Das Stück ist durchgefallen", but the use of the nominalization "Durchfall" does not seem to be popular any more. The only relatively recent example I could find is the review Kipphardts Durchfall by Hellmuth Karasek which appeared in DIE ZEIT on May 19, 1967.
However, in the 19-th century it was quite common to use "Durchfall" in this context. Here are some examples.
- In Recensionen und Mittheilungen über Theater und Musik from 1861 one can read on p. 563
Hamburg. - Das Thalia-Theater brachte nach dem unvermuteten Durchfall von O. Ludwig's "Erbförster" vier einaktige Novitäten ...
- In Rudolf Presbers book Vom Theater um die Jahrhundertwende which appeared in 1901 one can read on p. 161
Der "Vielgeprüfte" von Wilhelm Meyer-Förster ist in Wien durchgefallen. Es war sogar, was man so sagt, ein "böser Durchfall". In Berlin ist er beinahe durchgefallen. Also ein "guter Durchfall".
Der Wiener Durchfall is zu begreifen, denn es sind durchaus preußische Zustände, die da geschildert, gegeißelt, belächelt werden.