Surprisingly it's already mentioned, but hands down the whole Malazan Book of the Fallen, all ten of them, by Steven Erikson (hardly surprising with my s/n)
Worthy of a mention: Ian C. Esslemont (also in the Malaz realms). Jacqueline Carey, K. Arsenault Rivera, Mervyn Peake, Clive Barker (when's the third Arabat coming?)
And on the other end of the scale. Worst fantasy writer (even though the two books he's written are fabulous, but it was meant to be a trilogy) Patrick Rothfuss. And worst fantasy series, by far, Gor! That's the books, dear folk, not the world itself. The readers and online Goreans have made it so much better.