Do yourself a favour. This movie is an experience and as such, it should be lived without having anyone try to set your expectations on your behalf beforehand.
So if you haven't watched it yet, stop reading reviews and go in blind as soon as time allows you. Not for the possibility of a spoiler as much but for the mere descriptions of the setting and mood that are bound to place you in a certain mindset, no matter your will and conviction.
Do it right and when you're done you'll be left with the added bonus of knowing that when you inevitably rewatch this, not only will you get to re-experience it, but it will be anew, from a different angle, something that renders A Pure Formality... a... well... bogof deal, I suppose.