Like the loyal German bourgeoisie in 1945, trying to keep patriotically cheerful despite the distant ominous rumblings of Russian tanks, we Tarantino fans have kept loyally optimistic on the Croisette this week. We ignored the rumourmongers, the alarmists and defeatists, and insisted that the Master would at the last moment fire a devastating V1 rocket of a movie which would lay waste to his, and our, detractors. But today the full catastrophe of his new film arrived like some colossal armour-plated turkey from hell. The city of our hopes is in flames.

Quentin Tarantino's cod-WW2 shlocker about a Jewish-American revenge squad intent on killing Nazis in German-occupied France is awful. It is achtung-achtung-ach-mein-Gott atrocious. It isn't funny; it isn't exciting; it isn't a realistic war movie, yet neither is it an entertaining genre spoof or a clever counterfactual wartime yarn. It isn't emotionally involving or deliciously ironic or a brilliant tissue of trash-pop references. Nothing like that. Brad Pitt gives the worst performance of his life, with a permanent smirk as if he's had the left side of his jaw injected with cement, and which he must uncomfortably maintain for long scenes on camera without dialogue.

And those all-important movie allusions are entirely without zing, being to stately stuff such as the wartime German UFA studio, GW Pabst etc, for which Tarantino has no feeling, displaying just a solemn Euro-cinephilia that his heart isn't in. The expression on my face in the auditorium as the lights finally went up was like that of the first-night's audience at Springtime for Hitler. Except that there is no one from Dusseldorf called Rolf to cheer us up.

Pitt plays Lt Aldo Raine, the leader of an anti-Nazi commando unit whose avowed mission is to get 100 Kraut scalps apiece; we see the scalpings in full, gruesome detail, yet that figure is entirely forgotten about by the end. Mélanie Laurent plays Shosanna Dreyfus, a beautiful young Jewish woman whose family were slaughtered by SS Col Hans Landa, played by Christoph Waltz. She got away and (somehow) attained not only a new identity, but also ownership of a Paris cinema which is to play host to the premiere of Dr Goebbels's latest propaganda movie, in the presence of the Führer himself. Her plan is to incinerate the entire first-night audience by bolting the doors and igniting her vast inflammable stock of nitrate film. Meanwhile Lt Raine has his own plans for killing Hitler at the movie theatre and the Brits get involved too, in the form of suave Michael Fassbender as Archie Hicox, a crack commando making contact with exotic spy Bridget von Hammersmark, played by Diane Kruger.

There are some nice-ish performances, particularly from Fassbender and Waltz, but everything is just so boring. I was hoping for Shosanna at least to get a satisfying revenge on the unspeakable Col Landa. But no. The two Hitler-assassination plots cancel each other out dramatically and the director's moderate reserves of narrative interest are exhausted way before the end. He should perhaps go back to making cheerfully inventive outrageous films like Kill Bill. Because Kill Adolf hasn't worked out.

• Peter Bradshaw is the Guardian's film critic