That is interesting, I for one find it somewhat banal. It even gets worse when girls' choir starts to sing "lalala"s near the end.
Yeah, the lalala's aren't great (though I "get" why they needed to be there). This version here is the theme they play at the end of the movie. The version at the beginning of the movie does not have a flute and instead is *all* "lalalala's" and I'm not fond of that version. Obviously it's supposed to sound creepy and innocent at the same time. I think he did a good job, though.
But it's the flute that gets me. I just find it to be a sad and beautiful melody.
Generally, the movie itself is boring, I was disappointed when I finally watched it - nothing scary there at all.
The first couple times I saw the movie it was kinda scary. But I've seen it so many times now the effect has worn off. I think you also need to take into account this was a Spielberg movie. Horror flicks weren't his "thing," so it's no surprise it's not your typical scary movie. As much as the horror aspect of it, the other main theme of the movie is the parent's dedication to their child, which is a very Spielberg-esque thing. His movie "AI" is somewhat similar in that regard, even though the contexts of the 2 movies are entirely different.