Between Worlds, an English National Opera (ENO) production at the Barbican in London, "tears at the heart", wrote the Daily Telegraph's Ivan Hewett.
The opera, wrote Michael Church in The Independent, "reflects crazy courage" and "comes across with awesome power".
The Guardian, though, said it was not "as affecting as it ought to be".
Nor is there any "real sense", wrote Andrew Clements, of the "sheer chaotic terror" of the events of 11 September 2001 dramatised by composer Tansy Davies and librettist Nick Drake.
The Arts Desk also found fault with Deborah Warner's production, saying it is "peppered with problems" that include a "lack of clarity" and "monochrome pace".
"As a meditative lament on this human tragedy, Between Worlds succeeds," wrote Jessica Duchen.
"But as a metaphysical drama of the day itself, there is more to question, and much to clarify."
Between Worlds, the second ENO production to be co-commissioned by the Barbican after 2013's Sunken Garden, runs until 25 April.
It is the first opera to be written by Davies, a previous winner of the BBC's Young Composers' Competition who has written works for the LSO, the City of London Sinfonia and the BBC Symphony Orchestra.
An opera about people trapped in one of the Twin Towers during the 9/11 attacks has been called a "remarkable piece of work" by one UK critic.