I usually enjoy Rosalind Laker books with To Dance with Kings being a huge favorite. I've read a few others and enjoyed them but Banners of Silk was just terrible. I remember hating the characters and being bored stiff at the same time.
Another was Patricia Ryan. She wrote my all time favorite Historical Romance, Silken Threads, but followed it up with a terrible sequal, The Sun and the Moon. I've read a few others by her and while none are as good as Threads they were all decent. I'm not sure what happened with Sun and the Moon.

If I think of any other authors I'll list them here!