Isherwood is pretty straightforward in saying this will never be considered a great musical while saying that he also completely enjoyed himself. The Times, while often criticized for being self-serious, have long had a willingness to show appreciation for shows that don't intend to be anything other than a good time (see also: Rock of Ages, Mamma Mia, etc.).
For what it's worth, I had a really good time at Disaster. It's intentionally silly, and while it grated on my nerves off-Broadway, I thought this particular cast raised it to the level of pure pleasure.
We will all find shows that critics love that we hate and vice versa. Most recently for me, Brantley's rave for Whitaker in Hughie left me baffled. But it's silly to think that just because we don't always agree with their takes, they're somehow terrible at their jobs.