Just to throw in my 2 cents-worth, I was sorely disappointed with the American version versus the original. The American version seemed to be trying too hard, whereas the original seemed much more natural with a better mood and overall impact. We bought the American version used, and will more than likely be selling it back this week.
No accounting for taste, of course, but I do disagree... I think the American version really managed to achieve the same mood, the same sense of quiet dread that the Japanese version was so effective in creating.
For myself, I couldn't say which I prefer, only that I like them both. Certain details were better in one or the other of the two, or at least I preferred them, but both films are mightily effective, particularly in how they played with genre expectations while delivering "sincere" chills, all without going completely arthouse. Considering how rote and unimaginative most of the horror genre is, I don't really mind having two good versions of the same exceptional film!