Making a historical drama that purports to be based on truth is a tricky business. The tendency is to puff characters up to the point where their on-screen charisma stands out like a wristwatch on a Roman centurion, or to play fast and loose with the facts to jazz up the story.

Downfall, a dramatisation of the last two weeks of Adolf Hitler and the Third Reich, can't go there. The Holocaust may be fading from the collective memory (much to the horror of those who survived the nazi death camps), but six decades since the war ended, it seems to have become more, rather than less, politically sensitive. Especially if you are a German filmmaker.

Oliver Hirschbiegel's film, set in large part in the claustrophobic confines of Hitler's bunker as the Allies close in, interprets events with a rigorous attention to detail that is commendable. There is an atmosphere about this film that is unique to the genre of World War Two dramas. The fact that it takes a German perspective, with a large German-speaking ensemble, undoubteldy is what helps make it so intensely watchable. It's rare to see German filmmakers venture into this period, particularly where the focus is Adolf Hitler himself.

That criticisms have been levelled at the film because it doesn't highlight the gruesome reality of Hitler's Final Solution is understandable. But in attempting to show the man behind the monster, it still leaves you in absolutely no doubt about the chilling brutality of his reviled regime and of the man himself.

Bruno Ganz's performance as Hitler is a brilliant study of surface charm and reserved friendliness, that can switch in a second to explosive vitriol and demonic rage. It seems strange that this brooding, isolated figure who haunts the dimly lit corridors of the bunker, one arm quivering behind his back from advancing Parkinson's disease, could command such awe and respect. Yet, when all is clearly lost, including Hitler's marbles, few have the temerity to speak up against him. Easier to indulge his fantasy that he has armies to wage war up above rather than risk incurring his wrath. Such was the myth and fear that surrounded Der Fuhrer.

Bernd Eichinger's screenplay credits two main literary sources: the account by Hitler's last secretary, the late Traudl Junge, Until The Final Hour (Bis zur letzten Stunde), which was the source also for the critically acclaimed documentary Blind Spot - Hitler's Secretary (Hitlers Sekretarin) and the book Inside Hitler's Bunker by renowned Hitler biographer Joachim Fest.

Junge's (Alexandra Maria Lara) story bookends the film, starting with the moment when Hitler first chooses her as his secretary from a line up of girls in 1942 (because she is from the Bavarian capital Munich), moving to the final days in the bunker when the Fuhrer has transformed to a pallid, stooped figure raving maniacally at the traitors and weaklings that surround him, and closing by showing how Junge survived the final onslaught.

Junge's suggestion that Hitler's true nature only slowly dawned on her because she was too naive to initially see past his great man status may seem a little hollow, bearing in mind how rabidly anti-semitic her employer was. But her uncritical eyewitness account - she only left the bunker after Hitler's suicide - offers many intimate details about those last days, down to Hitler's table manners and how she would sneak up to ground level for a smoke with Hitler's devoted fiance Eva Braun (Juliane Kohler) when the shelling stopped. Smoking disgusted Hitler.

Braun, wearing her traditional Bavarian dress and a brave smile, or madly rallying staff to party even as the bunker shudders from explosions, comes across as a sympathetic character even. Her relationship with Hitler is one more of the true believer, than a lover. As she confides to Junge not long before her death, Hitler shows more affection to his dog Blondi.

This disturbing romance is brought painfully into focus when, kneeling at Hitler's feet, she pleads for him to spare her sister's husband, the careerist SS officer Hermann Fegelein (Thomas Kretschmann). Hitler, by this stage seeing enemies-within everywhere, spits angrily that Fegelein is a traitor and must be shot. Braun wipes away the tears. "Du bist Der Fuhrer (You are The Leader)," she suppliantly accepts.

Her tragedy is that she is loyal, unquestioningly so to the end. The larger subtext to this humane history is that Braun's tragedy was shared by a generation weaned on National Socialist ideology and terror. The film is littered with suicides - Hitler youth, young officers, guilty nazi top brass - but the caustic nature of nazi ideology is most forcefully brought home when Magda Goebbels (Corinna Harfouch), the fiercesomely zealous wife to Propaganda Fuhrer Joseph Goebbels (a deathly Ulrich Matthes), methodically drugs and then poisons her large brood of children rather then let them live "in a world without the NSDAP".

While the nazi top brass get drunk on champagne and schnapps and discuss the best ways of topping themselves, we also see Berliners scrabbling about in the rubble of the capital for survival. Russian artillery shells and soldiers bear down on one side and nazi lynch mobs ready to string up "deserters" who refused to join the Volkstorm (People's fight) are on the other. This desperate last struggle is poignantly conveyed in the story of a boy soldier, Peter, whose veteran father urges him to quit the barricades and come home.

The film highlights the difficulties in creating a factually based historical drama when most of the key players died before accounting for themselves. Albert Speer (Heino Ferch), Hitler's favourite architect, survived the war, stood trial and wrote in depth about his experience. He comes across as an ambivalent figure, despicable for his favoured status with Hitler, but almost heroic when he disobeys Hitler's orders to follow a scorched earth policy that would have killed many innocent Germans.

Another subplot about Professor Schenk (Christian Berkel), an SS doctor, who risks his life to help the wounded has been criticised for glossing his character - the man was apparently linked with medical experiments on prisoners in Dachau.

Ultimately, the film's shortcomings are far outweighed by its achievement as a serious and compelling insight into this dark era in Germany's history.