Here is a fierce, jagged shard of autofictional rage from the Israeli director Nadav Lapid, the winner of the Berlin Golden Bear in 2019 for his previous movie Synonyms. There is some really distinctive film-making language here, with the looming, uncontrolled closeups, whip-pans between characters for dialogue scenes, the throbbing sound design and some really sensational musical set pieces.

But the mystery and the unprocessed anger that make this film interesting all come at the beginning. As it begins to explain more and more about what drives its leading character, the film becomes less and less interesting and the stridently melodramatic finale, as well as being highly unlikely in ordinary plot terms, feels a little bit self-exculpatory.

The central character is a successful movie director, played by Avshalom Pollak, who has just had a great hit at the Berlin film festival. Now he is developing a project about the young Palestinian activist Ahed Tamimi, who went viral after slapping an Israeli soldier in front of news cameras and was finally imprisoned. The director wants to take as his starting point one Israeli man’s angry tweet that Tamimi should be shot in the knee and the film-maker seems to be working on images of knees – more like a video artist than a movie director – focusing on the fragility and vulnerability of human bodies generally in the face of state cruelty. It’s an aesthetic that the film we are watching seems itself to share.

But perhaps to give himself a break from the strain of working on this, the director accepts an invitation to attend a government-sponsored special screening plus onstage Q&A about his last film, at, of all places, a small library in the remote desert valley of Arava, south of the Dead Sea basin. This is where he hails from and the place brings back ugly memories. His librarian host is a young woman who is also a fan of his, flirtatiously played by Nur Fibak, and it is to her that the director confides a memory of bullying and abuse while doing his national military service.

So much is seething and boiling in Ahed’s Knee, so much pain and much self-reproach as he circles around the thought that by rising to national pre-eminence he has become complicit in abuse, a process that started while he was in uniform. The film achieves its own kind of release or scornful euphoria when it bursts out into music – especially one amazing flashback scene when the soldiers all dance together.

But this is not about Ahed’s Knee or Ahed’s anything very much. It is about this angry, film director who feels the need to confront his host, and himself, about their role in the system. But might he not thereby expect also to be forgiven, or at least have his pain acknowledged?

At first, we seem to be watching a very contemporary, very uncomfortable spin on 8½ or Stardust Memories; the artist himself consumed by his own doubt, his own memories, maybe by his own artistry. And while we are immersed in this traumatised situation, Ahed’s Knee is fascinating. But then we reach a stage where the lead character is monologuing heavily to explain everything and the battle lines are very familiar. Yet this disappointing ending can’t efface those flourishes of brilliance.

• Ahed’s Knee screened at the Cannes film festival and is released on 18 May on Mubi in the UK.