I fully anticipate some hate in my direction, as some people have really taken to this film, but I have to say that it has just never done anything for me. I first watched it a couple of years ago and I had to force myself to finish it, for the sake of finishing it, but I was overwhelmingly bored. I returned to it again this afternoon (with a little bit of an older head on my shoulders :)) and I feel I can sort of offer a little more than 'boredom' as a comment.
I think you have to start off be coming to this film with the right preconceptions, or at least not the wrong ones. It doesn't fit the same 'type' of J-Film as the Grudge or Ring, there are deaths but it's not some vengeful she-ghost hunting you for eternity, this film tries to utilise a different sort of 'horror', on a more emotional or psychological level by focusing on very everyday human fears such as death, the afterlife, and loneliness.
It's interesting to see how (although much of the technology in the film is now very dated) some of the comments on it - such as those about how the internet doesn't really connect people - are still quite valid. But one of the problems I came to realise that I had with the film is that its message of an isolated world, with people ultimately being unable to face existing alone any more, felt too forced. It was alluded to or actually stated by the characters quite repeatedly, it was unmistakable what they were trying to 'say', and the more they said it the more depressed I felt.
I wasn't scared by the thought, I wasn't horrified or disturbed I just felt a bit blue. Watching the world become less and less populated just felt a little too unbelievable, I felt I was watching a film taking place in some kind of parallel Earth, I felt distanced from it and that distance just sort of numbed the impact.
One of the things I did like were the two separate stories playing alongside each other, and the meeting up, but I felt that the male student's story was far more engaging than the co-workers, they never seemed to progress in the story, they just kept dropping out one by one until the requisite one was left behind.
I also have to agree that some of the film is beautifully shot, but to balance it there are also lots of grey scenes (some of which are quite hard to see), intended I think to add to the isolated, cold, world, but it's not really enough to break up the film or to keep it visually exciting. You can only sit and watch people having conversations, or wandering around unhappily, for so long. The use of music is very good, actually lifting up some scenes and making them quite memorable (I'm thinking of the jumping woman, for those who have seen it). But there seem to be quite long periods without it, or where it isn't used to contribute at all.
I'm not saying that this is a horrible film, but I'm trying to balance out that it won't suit some people. Rent it first if possible, this isn't the kind of J-Horror film (can we call it horror?) that all films seem to be marketed as at the moment, it really might work for you, but it just didn't have the effect on me that it seems to have done on others here.