While I can't access all the reviews Les Miz got when it opened on Broadway in 1987, and they were not unanimously favorable, they were mostly favorable, led by a seriously ecstatic Frank Rich rave (and that really meant something then, although the advance was probably big enough that a mixed or even negative review might not have hurt that much). Variety's tally (not that the trade rag's tallies have always been terribly accurate) was "12 favorable notices (Rich, Times; Barnes, Post; Kroll, Newsweek; Henry, Time Mag; Curry, USA Today; Langfield, WABC-Radio; Hamburg, WOR-Radio; Lyons, WPIX-TV, CBS-Radio; Siegel, WABC-TV; Granger, WMCA; Raidy, Newhouse chain; Kuchwara, AP), six mixed (Wallach, Newsday; Feldberg, Record; Winship, UPI; Simon, New York; Lindstrom, WNBC-TV; Snow, WINS), and four unfavorable (Kissel, News; Lida, Women's Wear Daily; Cunningham, WCBS-TV; Klein, WNYW-TV)." And I'd say that it was effectively 13 favorable notices among the critics included in the tally since Lyons was on two different networks.
It won the New York Drama Critics Circle award for best musical with 11 votes. It was followed by Me and My Girl with 8, and Rags (which opened today back in 1986) and Three Postcards each getting 1.
Lest any foolish person think that I write this because I'm a fan of Les Miz, I'm so not a fan that I don't even own a recording of it (and I never have).