*Still in box*
Oh yes....! Real nasty in places.
Never watch it alone in a darkroom with loud digital surround and then go to be alone in your place with nothing but your scene-photographic-memory to ambush your every thought as you attempt to get to sleep. (If you can even go into your darkened bedroom....)
If you allow yourself to get into it, it can be one of the most disturbing films of its type.... The US remake is pretty good too. (Even joltier.)
People gave it mixed reviews due largely to their disappointment with having to work out the non-linear plot and of course those who went with chatty friends keeping the atmos from taking hold...
Definitely best enjoyed in the first described-trauma-inducing conditions...