I just saw this last night. I have to say, my relationship with it is complex right now. I hated it most of the time. By the time the end credits ran, and I turned it off, I still hated it. A couple of hours later, I started to think that it was actually pretty damn brilliant. I'm sticking with the latter analysis.
Yes, it was deeply unpleasant to sit through, and there were moments when I seriously wanted to turn it off, a reaction I have rarely had, and I sat through House of the Dead. I felt that it was pointless, wallowing in misery for no good reason. I guess the reason was just slow in coming to me.
I know nothing about Haneke, I've never seen another of his films. But if I had to venture a guess, I would imagine that he actually hates films like this, and is trying to make us question why we would sit through it, if not actually punish us for doing so. Every time the antagonist turns and speaks to the audience, we are incriminated in the tortures that the family is undergoing. The question "Why the hell would you want to sit through this?" is in every scene, and it's very intentional.
Incidentally, I seem to have a somewhat different take on the rewind scene than you guys do. It's not just a matter of the audience finding pleasure in watching a grisly death. Anna blowing away a tormentor is the moment of cathartic vengeance that we fully expect in this situation, the moment that allows us to sit through all the unpleasantness. We wait for it as if it justifies everything, and we feel better about ourselves because evil has been punished. But Haneke denies us this moment of closure. Sorry, but you came here to watch this sick shit, and you're not going to be excused. It's going to its only logical conclusion whether you like it or not.
I'll probably never watch this again, and I probably won't bother with the remake. But damn, I do admire it.