Tad Williams has a lot of interesting stuff in his arsenal. Memory, Sorrow, Thorn is notoriously wordy but is also an absolute classic of the genre and inspired GRRM to start ASOIAF. There's also a sequel series, a prequel, and a bridge book in the setting. Otherland is sort of sci-fi mixed with fantasy and is apparently really good but I haven't read it. I don't know much about his other stuff other than Shadowmarch is not as good as his other series. His writing has kind of a Robert Jordan quality to it where it can be quite slow but his character work is miles ahead of Jordan.
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