I mean the last statement not in terms of cinematic or narrative merit, but in terms of approachability and ultimately economy. The psychedelic imagery, the archaic dialogue - these can all be off-putting, but nothing has confounded critics & viewers as much as the morality.
Attempts to grapple with the moral stance - or lack thereof - of the film has produced separate extremes. I have seen some critics labelling the film simply amoral, almost Nietzschean, whilst others describe it as a cast full of despicable people. Both are wrong.
The simple truth is that the Northman IS a moral tale, deeply so, & one full of people who are, within the norms of their culture, either perfectly decent or at least understandable. But it is their culture, not ours. It is an honor culture, like most in history, but not ours.
Norse masculine virtue was imagined chiefly in terms of the dichotomy of drengskapr and níð. A níðingr (or nithing) was a person afflicted with dishonour - either through his own dishonourable conduct OR through lack of socially mandated honourable actions.
A nithing, then, was a coward, a weakling, someone treacherous, pathetic, and generally to be despised. He was a man who through his own action or inaction had placed himself beyond the moral horizon of his society and shown an utter lack of *drengskapr*
The word 'drengskapr' and the base adjective 'drengr' has been translated in various ways over the years, from 'valiant' to 'virile' to 'chivalrous'. Probably Medieval philologist Tom Shippey renders it best in his work Laughing Shall I Die as 'laddishness'
To be a drengr was to be an utter lad, with all the connotations that carries. This is the skeleton key to the Norse mentality. The Viking world was one wherein the brash, brave and violent conduct of boisterous lads was the utmost mark of personal virtue.
What this means, in terms of understanding The Northman, but also the authentic Norse sources, is that raiding, pillaging, feuding, belittling and even slaving were, within that culture, fine. What mattered was bravery, determination, and to face death with insolence and humour.
What The Northman perhaps does not capture so well is that the Norse were a rather funny culture. Humour were important and never beneath you. Their jokes could be esoteric or downright scatalogical - what mattered was getting the last laugh. They were brutal, but not dour.
Yet an enemy that is laughing, jeering & mocking even as they slaughter your family and sell you into slavery is hardly likely to register as an affable bunch. The highest value in Norse society was, as noted, personal honour, and nothing was more important than avenging slights.
This brings us at last to the ethics of The Northman. What Amleth's uncle inflicted upon him when he killed his father and took his throne was a níð. But, even more crucially, if Amleth had failed to avenge his father, it is AMLETH who would have been a níðingr
Reviewers have spoken of Amleth's failure to constrain his hate, his self-destructive behaviour, and his personal failure in choosing revenge over his love for Olga. But this is to misunderstand everything. Amleth never had a choice. He realises this at the end.
Amleth's actions in harassing Fjölnir at night & in secret rather than openly confronting him was already shameful by their ethics. Had he then simply abandoned his uncle and left to live with Olga, she would have been the wife of a nithing, and his children the offspring of one.
What Amleth manages to do, and what was in fact the very greatest degree of flexibility his culture allowed, was to UNIFY his love for Olga with his duty of revenge. In choosing both, he proved his drengskapr by avoiding the twin níðs of cowardice and infidelity
I am not saying any of this is objectively morally good. I do not belong to Amleth's culture. I do not share his values. But one cannot expect him or anyone else in his day to conform to the morals of another age and another faith. Amleth, in the end, proved himself a lad.