The Forgotten is nothing like The Sixth Sense and to suggest otherwise is reductionism at it's worst.
If anything, the most appropriate [reductionist] synopysis, and quite possibly the studio pitch, would be to say that it's like Ransom crossed with the X-Files, with a strong female lead. Of course, that probably wouldn't sell very many tickets as an ad campaign! Unlike the Sixth Sense, though, the ill-conceived trailers for The Forgotten, while incredibly effective as attention-getters, leave very little room for any mystery regarding what's actually going on. You know pretty quickly that there can only be one explanation, but it doesn't ruin the movie as it's much more about the journey than the final destination.
I'm not going to spoil anything here, but I will say that the broadside car crash and people getting abruptly snatched into the air remains startlingly effective even though you know they're coming. And reviewers that complained about the "cop-out" ending are either cripplingly cynical, or just really hate kids.
Strip away the spooky X-Files wrapping and, at it's core, The Forgotten is a really well-made Lifetime TV-movie about the bond between a parent and a child; in particular, that between a mother and a child. What makes it work, though - and yes, it does work - lifting it beyond anything Lifetime could ever hope to produce, is Julianne Moore, who ably carries the movie on her freckled shoulders. The X-Files wrapping keeps it from being written off as a chick flick.
Moore's tentacled anguish over losing her son - complex and well-acted, never approaching Mel Gibson's Ransom histrionics - and the realization that someone/thing is messing with her head trying to make her forget him, makes the movie's more extraordinary elements both believable and more exciting. The explanation, all the more effective for it's being offered rather matter-of-factly, puts it more along the lines of The Village than Sixth Sense, with the story revolving around a philosophical question as opposed to a simple gotcha! twist.
Novel concept that!
Random trivia: The Forgotten's writer, Gerald Di Pego, also wrote the teleplay for The Death of the Incredible Hulk, as well as Phenomenon, which had the tagline: "Some things in life just can't be explained."