I absolutely adore the “Dark is Rising” books.
https://en.m.wikipedia.org/wiki/The_Dark_Is_Rising_Sequence
Like the Hobbit/LOTR, Book 2 is really the start of the main story - but the characters in Book 1 come back later on. At the time I had connected them more with CS Lewis’ stuff, but they are way more folklore-based, like LOTR.
They are supposed to be Teenager/high school books but they are just as involved and deep (and dense) as Tolkien. Not George R R Martin level - I’ve never been able to get into his pace... of... needing... 15 ... pages... to write ... what... could have ... been .. conveyed .. in ... 2 ... sentences...