Okay, so everyone else pretending to be Tolkienesque had better queue up behind Kay because he sets the bar HIGH, my friends.
Not that I would expect less from someone who worked on turning the Silmarillion into something publishable, but still.
The thing is, Kay does with the Celtic mythology of what is now the UK more or less what Tolkien does with Anglo/Germanic mythology. They are both, in their own way, turning their own mythologies into a greater narrative past. They're also both invested in telling the story of the last stand of the light against the dark (I suddenly want to reread Susan Cooper. Weird.) and what that looks like and what sacrifices do (and do not) get made and it's also REALLY interesting to see how the difference in source material changes the fulcrum on which the world turns. There's a conversation to be had about the difference between mercy and sacrifice and I have to think harder about it.
But they're also very different books with a very different fellowship at the heart and that, as they say, makes all the difference.