I heard that this movie ranked in box office sales on its opening weekend in the United States...that makes me conclude that the movie have something to be impressed of...
It made $50 million, which is quite good, sure, but it dropped off very quickly after that, and concluded with $114 domestically. Most films finish with roughly three times their opening weekend gross; anything less generally indicates poor word-of-mouth.
It wasn't just front-loaded in general, however; it was front-loaded even on its first weekend, making $20 million of its $50 million on the very first day. That generally indicates a film with a very fervent fan base, which, in turn, generally implies that it doesn't have a terribly broad appeal.
However, given director M. Night Shyamalan's financial success with
The Sixth Sense and
Signs, it was widely hailed as a disappointment, both financially and (moreso) critically. I myself thought it was solid; certainly an above-average film, but definitely one that would have been better-received with the many preconceptions people brought to it. It probably didn't help that someone on this forum (in this very thread, I think) spoiled the ending for me before I saw it.