Praise for The Lives of Others, particularly from Germany, comes partly at the expense of Goodbye, Lenin!, a 2003 box office success at home and abroad, which skipped lightly over the dark side of East Germany. "Stasi without Spreewald gherkins", was one headline describing The Lives of Others, referring to the Communist east-gherkins which one of the characters in Goodbye, Lenin! famously yearns for. The Spreewaldgurken have come to seem a synonym for the much despised Ostalgie - nostalgia for life under Communism.

Goodbye, Lenin! (though in reality not as rose-tinted as critics of the gherkin episode might suggest) is certainly less dark than The Lives of Others. Its comedy, though directed (like The Lives of Others) by a west German, is a partial defence of east Germanness with a small e - the now beleaguered identity, not the capitalised one-party East German state. By contrast, The Lives of Others is forensically clear in portraying the inhumanity of the Communist state.

It tells the story of the successful playwright Georg (Sebastian Koch) and his actress girlfriend Christa-Maria (Martina Gedeck), who are about to be forced into a drama which is none of their making. The bejowled culture minister, uninterested in culture and played with hideous sliminess by Thomas Thieme, uses his untrammelled power and zero charm to force Christa-Maria into unwanted trysts. He lays the groundwork to get his rival out of the way, installing round-the-clock surveillance in the couple's apartment.

The plot contains a series of unexpected twists and turns - comic and tragic alike - after a hitherto loyal Stasi (secret police) agent (Ulrich Mühe), instructed to listen to the couple's every word, finds himself doubting the regime he has served so well. The film effectively becomes (to quote a title that recurs in different contexts in the film itself) the "Sonata of a Good Man."

The storyline does not require that the audience should understand (or even be especially interested in) how East Germany worked, for the film to be engaging. It works powerfully at an emotional level - as a story of trust and betrayal, of self-respect lost and redeemed.

It is this sympathy for the real dilemmas faced by ordinary East Germans - as much as its much-touted willingness to explore the Communist darkness - which makes this film truly different from what came before. For many years after German unity, the shorthand "IM" - inoffizieller Mitarbeiter ("unofficial collaborator", or Stasi informer) - was the dirtiest of dirty words, in public discussion in Germany. In many respects, this was understandable. The IM network was, after all, at the rotten heart of the regime. No depths were left unplumbed. As the Stasi archives later revealed, best friend reported on best friend, spouse on spouse.

For the German (in other words, west German) media, this was an issue of absolute clarity. Little distinction was made between those who were shameless, on the one hand, and those who were spineless or hapless, on the other. Thus, the author Christa Wolf stood revealed as an IM a few years after German unity. Her moral authority was obviously tarnished by the knowledge of collaboration. In addition, though, western critics seemed almost gleefully to spend page after page shredding her reputation - even though the files showed that Wolf's career as an informer had been unimpressive and brief. (The east German public, interestingly, seemed to rally to her more warmly than ever, when the attacks on her were at their height.)

Some of the criticism of those who collaborated came from former dissidents, whose own stance gave them the right to pronounce judgement. Many of the harshest judgements came, however, from westerners who had never faced a moral-political dilemma in their lives, but none the less felt they knew everything.

The spied-upon Georg has never been an imprisoned dissident in the mode of Vaclav Havel or Alexander Solzhenitsyn. On the contrary, he is acclaimed and rewarded by the regime. (In a nice touch about the ironies of living in a dictatorship, he owns a Solzhenitsyn novel which he received as a gift from Margot Honecker, wife of the much loathed Communist Party leader Erich Honecker.) Even Georg's friend, who commits suicide because of his ostracism by the regime, has tried to ingratiate himself, and failed. Later in the film, we see unfolding in compelling detail the torturous blackmail that can lead an otherwise moral character into collaboration.

IMs could destroy lives. But there were different circumstances in which people became IMs in East Germany. The prolonged failure after 1945 to confront the Nazi past - in other words, the murder by Germans of millions of "others" - was a problem for Germany, in its decades-long search for political stability. (It took a quarter of a century for confrontation with Hitler's legacy seriously to begin.) But the complacent western finger-pointing through the 1990s about a country where Germans were perpetrators and victims alike was almost as unhelpful as the earlier lack of confrontation had been.

Zivilcourage - the bravery which allows a person to do the decent thing - is needed in every society, as the Germans know better than any nation in Europe. But Zivilcourage does not mean complacently pointing fingers at others. The lives of others, as this film powerfully reminds us, always remain partly unknown. We may seek to judge our own weaknesses. Judging the compromises made by others in an authoritarian system is more difficult, by far.