I absolutely loved the first in this trilogy (The Wizard of Earthsea) but The Tombs of Atuan even surpasses that! As others have said, the story itself doesn't really get going until half way through the book, but there is something deeply compelling about the way Le Guin writes and it certainly didn't feel heavy going at all. In any case, the latter half of the book is page-turningly gripping enough to make up for it! 
 I only wish I had discovered these books 20 years ago. Even though set in the fantasy land of Earthsea they speak great truths about the nature of dark vs light, freedom vs safety, and of trust and friendship. 
 Love, love, love.