In 2007, when this was made, it was the most expensive film ever to be made by the Swedish film industry, at around two million kroner. It's actually two films, which were also cut into six TV episodes, adapted from a book by Jan Guillou.
The cinematography is beautiful. Honestly, if the series were rubbish it would be worth watching just for the beauty of the shots. It was filmed in Sweden, Scotland (for monasteries and castles) and Morocco standing in for the Holy Land. The costumes are extremely good as well.
It started off in Swedish, with subtitles, but then Simon Callow appeared, as the abbot of a monastery, and he spoke English, and another monk at the monastery spoke French - and when they got to the Holy Land various characters, including Arn himself, spoke Arabic.
It's a love story - due to local politics, Arn and Cecilia are forced to do penance for their forbidden love for twenty years, Arn as a Knight Templar and Cecilia in a convent with an evil Mother Superior (who comes from the rival clan). Despite all their troubles, they never lose faith in each other, even though getting back together again is not as easy as it might be.
Any story involving the Knights Templar and the Crusades has to involve the Horns of Hattin - the disastrous battle (for the Christians) which Saladin won, after which Jerusalem was his for the taking. Sure enough, Arn gets to take part in the battle and not be slaughtered at the end as a Templar.
When he gets back to Sweden, he's involved in local politics again, defending the sons of his friend King Knut from the Svarker clan's takeover after Knut dies. There's a pitched battle in which the Folkunds are at a serious numerical disadvantage - but Arn didn't spend twenty years in the Holy Land twiddling his thumbs, and he comes up with the tactics that swing the balance in their favour. Some people have reviewed the film and complained that he invented Agincourt two hundred years too early, but his appreciation of the power of the longbow was well set up earlier in the story.
So, this is one of the more historically accurate films I've ever seen, with a good love story, exciting pitched battles and a hero who is straightforwardly honourable and faithful - a real old-fashioned hero, and a heroine who goes through terrible trauma to be true to him. I thought it was wonderful.