I read The Belgariad many years ago.
Mainly I remember it as having the most fully-drawn two-dimensional characters in literature. None of them was bad, but none of them really stood out as interesting new characters. Instead you had The Charming Thief, The Brash Warrior, The Young Kid From The Farm, The Snooty Princess, The Wise Magician, etc. That and the whole feeling that the collection of kingdoms was run by the Good Ol' Boy network -- heck, they came into international meetings and threw their crowns around.
So I enjoyed it as a fun little summer read, but nothing more, certainly nothing to really recommend to others. Did it "advance" the fantasy genre? Nope. Did it have deep characters or plot? Nope. Was it a fun, light read. Sure. OTOH, I don't own it anymore, and I keep most of my books.