I've liked some individual fantasy books, but the only series that stands out is A Song of Ice and Fire. I think that is because it is the kind of story I would write, had I any skill. It combines the elements I love creating in a fantasy world - complex cultures, politics, and history. And the conflicts are more personal or political, and aren't painted black and white; everyone is a shade of grey. And of course, George Martin is a talented writer. He describes things in a way that is sufficiently detailed but easy to read.

Every other series I've read has been lacking in some ways. I would love fantasy novels that read like something by Bernard Cornwell, but so far only ASOIAF has come close.