On the Backfires of Rave Reviews, ala Tom Rachman's "The Imperfectionists"

Why is it that the giddiest rave reviews often somehow make their books sound suspect? I note this just having read Christopher Buckley’s rave of Tom Rachman’s The Imperfectionists in todays NY Times.
http://www.nytimes.com/2010/05/02/books/review/Buckley-t.html?ref=books
The book does sound fun, but the reviewer’s exuberance, plus the waggish character names and plotlines, make me suspicious. A good example of this odd phenomenon—the literary equivalent of “She’s got a great personality!”—occurred last fall, when Jonathan Lethem reviewed Lorrie Moore’s new novel, A Gate at the Stairs, raving madly, the best novel ever written! (In contrast, a good friend of mine who read the book said, “It sucks.” I haven’t read it yet, but the hardback is here on my desk, and is next up in line.)