It has always been rather controversial; "long disputed and now refuted", as the famous Dutch Indologist Jan Gonda (Gonda 1971) sarcastically noted (cited as in Collinge 1985: 16). It seems though it is much less controversial now, at least among IE linguists. But the jury is still out.
Kurylowicz, Meillet, and Szemerenyi rejected it (not a bad company?). Even Brugmann himself eventually gave up on it.
Paul Kiparsky (Stanford) argues BL is a morphophonological process, not a phonetic law.
Lubotsky (1997) summarized its history quite succinctly:
"From the very beginning, however, BL was the subject of passionate debates. Whereas such scholars as de Saussure, Streitberg and Osthoff
accepted BL [...], the resistance was growing. More and more counter-examples were found so that Hermann Hirt (1913) was eventually able to present a list of 67 items. The large amount of exceptions and the severe criticism of his colleagues forced Brugmann to withdraw his Law. In 1921, Hirt wrote: "Das Gesetz ist tot, und es hat jedenfalls nicht zum Vorteil der Wissenschaft
gelebt, denn wir sind dadurch verhindert worden, eine ganze Reihe von Problemen in Angriff zu nehmen" (19).
Kurylowicz was able to give another life to BL in his 1927 article - even though he changed his mind about it twenty years later.
Collinge 1985 notes that
"Yet, despite the author's own renunciation, fighters on the law's side [...] continued to emerge - and still so continue" (p. 14);
or, to paraphrase Mayrhofer (Mayrhofer 1951), "the mummy has been brought into the light."
cf. "So bedarf es einer Rechtfertigung [...] die Mumie des "toten" Gesetzes noch einmal ans Licht zu ziehen" (Mayrhofer 1951: 9).
See Collinge 1985 for more details and a good laugh (I enjoyed his unusually candid style of writing).
Götz Keydana (in Keydana 2011) writes that
is "the most adequate and most widely accepted version" of BL (p. 2)
In his 2011 paper, he argues that by
"assuming BL as a sound law of PIIr. seems to be the best and least costly
way to deal with Vedic and Old Iranian /a/ from */o/.."
cf. Kiparsky 2010 who, on the other hand, writes that
"With Kuryłowicz, I believe it is not a sound change, but a morphophonological process that has been added to the inherited ablaut system within Indo-Iranian."