Several reviewers have already spoken of the powerful impact of this film as a document of the terrible atrocities of the Holocaust. What is perhaps most remarkable about this film (and that most reviews here have not remarked upon) is that it does not aim to reconstruct a past that is impossible to imagine, but to document the traces this past has left behind for the present, and to suggest that this unimaginable past is nevertheless not so far off. However difficult it may be to imagine being involved in such events (whether as victim or perpetrator) it is nevertheless true that those who were involved are not so very different than ourselves.
In other words, this is not just a straightforward documentary depicting the horrors of the Holocaust. It does that and does so in a way that is very powerful. But what makes the film distinctive is the way in which it raises questions, most insistently the question whether such horrors might be repeated. The film's major contention is that it is very easy to think that events like the Holocaust could never happen again -- that they are singular events and that the people who perpetrated them are monsters, unlike "us" -- but that this perception is a mistake. Many of the individuals involved in the horrible atrocities of the Holocaust were quite ordinary folk who loved their families. The point is that even your next door neighbor or anyone, under the right pressures, in situations where those they harmed had been dehumanized, could potentially also do such things.
The events at Abu Ghraib (and other contemporary atrocities) should remind that people we would otherwise think of as decent, upstanding, citizens are capable of horrible and repulsive actions. That the events in Abu Ghraib did not reach the scale of the events documented in this film seems to be a matter of degree and organization, but not a difference in kind. The film is perhaps more relevant and powerful today than ever. (This remark is not intended, of course, to minimize the scale and horror of the Holocaust; or to suggest that the systematic and planned massive scale genocide that took place in Auschwitz and other sites is on par with the contemporary practices of torture that appear much less systematic; still: that American citizen soldiers who by all accounts from friends and relations seemed like decent folk could find themselves able to participate willingly or even under some coercion or pressure in such horrible and degrading practices as were engaged in at Abu Ghraib and likely Guantanamo and other camps as well, is an indication that the cautionary remarks that end this film are still important).