- Animation Age Ghetto: Somewhat. It's recommended ages 5 to 7 on Netflix, despite the whole "vikings attacking and murdering an entire village" thing.
- Anticlimax Boss: Crom Cruach. Despite being an ancient Celtic god who destroyed Aisling's entire family (and possibly species), it gets about a minute of screen time and is promptly defeated by a piece of chalk.
- Awesome Art: The entire film is full of beautiful art that at first seems simplistic, but actually has a lot of details when you look closely... much like the art in the Book of Kells itself.
- Awesome Music: The entire soundtrack is great, courtesy of composer Bruno Coulais and Irish band Kila, but Aisling's Song is particularly noteworthy and regarded by some as the film's high point.
- Ensemble Dark Horse: Despite getting less screen time than Brendan and Aidan, Aisling is by far the most popular character in the film, even finding her way into Empire's list of 50 best animated movie characters. Compare the original theatrical poster◊ to the post-Oscar one. She also had the honour of going to the Oscars in 2010 when the film was nominated for Best Animated Feature. Word of God says here that Tomm Moore's thinking of doing a short film on Aisling or Pangur Ban, but he's hesitant about it because of people's head-canons.
- Fanon: It was a fan theory that Aisling lost her human form completely, as she only appears as a wolf to Brendan at the end.
- Genius Bonus:
- The first ink Brendan is sent out to gather materials from is based on a real medieval recipe for gall ink; the "berries" are actually used cocoons for a type of wasp. But the resulting ink is actually black.
- Aisling is shown to be frightened of the monastery's cross in the courtyard and is unable to enter the tower where Brendan is. Fitting, since she's a fairy and her people are slowly being pushed out and forgotten as Christianity spreads across Ireland. Fairies in Irish folklore were also unable to enter buildings unless specifically invited, thus the use of Pangur Ban to free Brendan from the basement.
- And, as mentioned above, the lavish detail the animators paid to the Book of Kells is gorgeous, and looks like it could easily be an excerpt from one of the pages.
- It's Short, So It Sucks!: Perhaps the most common complaint with the film. The movie features a rich story and world with monks, a wall, a sacred book, fairies, Vikings, and an Eldritch Abomination, but packs all of it into 75 minutes of screen time.
- Jerkass Woobie: Abbot Cellach post-attack, after he's been left broken by his guilt of not being able to protect his people and Brendan.
- Mondegreen: What Brendan prays on the stone in the forest. The subtitles say "Oh no, it's hard enough," one can hear it as "I know eternal love," and the DVD Commentary mentions that it's a prayer in Irish, which doesn't make sense with the English subtitles. It's the opening line of the Lord's Prayer in Irish: "Ár nAthair atá ar neamh...". The subtitles on the UK DVD just say [Prays in Irish].
- Narm: For some people, it's hard to take the plot seriously when some of the dangerous events happened all because Brendan wanted to to create a book.
- Smurfette Breakout: Aishling is by far the most popular character, and fans have been calling for a spin-off based around her ever since.
- Strawman Has a Point: Abbot Cellach's obsession with building his wall over preserving the books and his decision to forbid Brendan to go to the forest are portrayed as well-intentioned but ultimately misguided. And there's no doubt that he's not the best at expressing his affection towards Brendan. However, on the other hand, when Brendan does go into the forest, he's attacked by wolves and would have died if the local representant of the Fair Folk didn't come to help him. So the abbot was perfectly justified. Cellach's decision to protect the present (with his wall) instead of the future (the books and their knowledge) can seem justified in a time of invasions. And it's worth mentioning that, had he not lived in a world where Northmen are apparently unstoppable subhuman monsters, an invading army would have thought twice before attacking a heavily fortified location.
- Vanilla Protagonist: Brendan, not much to him except that he's nice and brave.
YMMV / The Secret of Kells