The Dark Is Rising Sequence by Susan Cooper

I used to love these books when I was about 13, and decided to reread them to find out if I was wrong, and I was very much not wrong. These, along with some of the Once and Future King books are the only Arthurian fantasy that I actually have time for. Susan Cooper is a real master of atmosphere; these books are imbued with a mysterious and almost numinous quality that echoes the Le Morte D'Arthur without losing touch with the present. A lot of fantasy books are ruined by the fact that magic in them is just not believable (if that makes sense), it's just a bunch of ridiculous forces and explosions and seems to just function like super-powerful machine guns or something. But the magic in these books is delightfully random, which is very much like original Arthurian legends, where things just happen in bizarre and fantastic ways, people go off on arbitrary quests, and weird objects appear and disappear seemingly without reason. These books have the same quality of the fantastic, it's both awe-inspiring and somehow believable. I used to think that these books were too Manichean (there's the Light, which is 'good' and the Dark, which is 'bad'), but reading them now, I can appreciate that it's much more complex than that. The Light and Dark are sort of like tectonic plates moving under the events of history, but the Light certainly isn't 'good' in any conventional sense. Will Stanton, who finds out at the age of 11 that he's not a normal boy, but one of the most powerful agents of the light, transforms over the course of the second book from a human into something that isn't really quite human any more. By the end, he doesn't hesitate to take a chance on possibly sacrificing his sister's life to thwart the Dark. I found it really creepy that the agents of the Light don't seem to be capable of forming affections like normal people do, or else they put their cause before their affections. The one serious criticism I have of these books is that they get too specific as they go on (which in my opinion, was what made the Harry Potter series devolve into disaster after the first book). Apparently the fourth book, The Grey King, is regarded as the best one, but I really like the first two best, because what is going on remains so mysterious. Once it gets into specifics of how magic works, of people warding off forces with their minds, of why certain things happen, it gets much less interesting for me. I really liked the books where causes remain hidden, where there's a sense of things lost forever and unexplained mysteries. The last book is definitely my least favourite, except for the journey in the Lost Land, where a lot of really bizarre and random and creepy things happen. I still consider these books absolutely genius, especially because Susan Cooper somehow manages to makes things like invisible swords, vanishing flames, shattering mirror mazes and alterations in space and time seem actually believable, rather than cheap conjurer's tricks. The characterisation is also wonderful, the dialogue is lively and realistic (in a lot of children's / young adult books the dialogue is just cringeworthy), and I could really believe in all the characters.