I'm not going to go too into depth about the plot of this film, since the external reviews cover it quite well. Like Andrés Wood's 2004 film 'Machuca', this film covers the political turmoil of the Allende years in a historically-informed and detailed way that you just do not see in non-Chilean films on the Allende and Pinochet years. As a history buff with an interest in historical revolutions and dictatorships, that in itself is a draw.
However, 'Araña' is not just a 1970s costume drama with political pretensions, but a well-acted drama giving an insider view of fascist activism and it's causes and ongoing effects in Chile's highly stratified class society. The historical drama part plays out a bit better than the contemporary political thriller one, but the film is still very worthwhile overall.
This film did not get any kind of North American release outside of the narrow film festival circuit (it's not even out on DVD), and my only guess is that distributors might have thought the plot was too specific to Chilean history for international audiences, or perhaps that a film that's antifascist but nevertheless is centered on fascist protagonists would not be well-received by 'woke' North American audiences.
As others have noted, this film is oddly very hard to find internationally. It's not on Netflix, nor HBO, nor Amazon Video. The only streaming version I could find is over the Australian service Stan, and for folks outside of Australia, one would need VPN to access it. I was only able to find it after, with great difficulty, downloading a high-resolution Spanish-language version on a Russian social media site, then with further digging, finding English subtitles for it and carefully re-syncing that to the video I downloaded. Some of the most trouble I've gone through to see a film, but I think worth it. In the end, though, it would be good if Netflix picked it up.