These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Critical Research Failure: Leaving aside the fact the Romans never got as far as Ireland - in fact Ireland was raiding Great Britain in the 4th century - Longinus was a Good Guy in Christian mythology!
Ensemble Darkhorse: Hands down the most popular character on the show was Vera Farmiga as Catlin.
In "The Chosen" a young boy believed to be the reincarnated father of the Druids is taken from his parents to the island of the Druids, causing much grief to his parents. After his father is killed by assassins, his mother travels all the way to the island where she is welcome to live among them.
In "Banshee" the gang help a young woman who foretells death return to her home in order to protect her from superstitious folk wanting to kill her. We never learn why she left in the first place.
In "Tash" - well, would you frequent a brothel run by a leper?
Les Yay: Catlin and Shannon only get two scenes together, but they're more than enough to qualify for Les Yay.
Replacement Scrappy: An unusual example. Though Catlin was never written out of the show, towards the end of the thirteen-episode run she seemed to be getting side-lined in favor of Fergus's daughter Molly, both as the lead female character and Conor's love interest. This did not win the character any fans considering Catlin's Ensemble Darkhorse status, and Molly's characterization as a Bratty Half-Pint.
Tastes Like Diabetes: Some of the dialogue, including sentiments like listening with your heart, believing in yourself and trusting in each other.