I'm into my 'J-Horror' at the moment, and have just finished up watching Dark Water. It's directed by Hideo Nakata, who directed the Ring and comes from the selection of short stores by Koji Suzuki. I must admit, it's one of the most nerve-wracking films I've seen for a while. Sheer suspense throughout. I'd definitely see it if your a fan of J-Horror, or horror in general. Also, don't be confused, and buy the English only version; be sure to get the original Japanese version, with subtitles; far better. There's some more extensive information here, but be warned, it's a spoiler: http://en.wikipedia.org/wiki/Dark_Water_(2002_film) Enjoy. PS - As anyone seen 'The Orphanage'? I'm just about to watch it.
Is this one of those films that are supposed to be the scariest film ever but then you see they have a 15 certificate?
I wouldn't say it was pant-fillingly scary. Japanese horrors tend to veer more towards the pyschological/suspense side of horror. This, quite frankly is one of the best out there for me. Another good one to watch, is a film called 'Audition'; that's genuinely twisted to the max. Good film though.
Audition is excellent I love his plan... but would you know it, things don't work out how he intended.