Several years ago I stumbled across Critters. You have to participate to have your own work critiqued, which you'll find with most workshops. You can specify that the works you crit are only fantasy, or you can configure a mix of science fiction, fantasy, and horror. There is a deadline for submitting your crits, so skip this one if you're low on spare time (that's the only reason I left). It's geared toward stories, but you can make arrangements outside the normal sequence to handle books.
Critters
Critters