I finished all four books of the Songs of Ice and Fire series that George R. R. Martin has written so far. Each book is two or three times the size of a typical book. Book four, A Feast For Crows, was not up to GRRM's usual standards.
One plot that I liked moved forward well (King's Landing). There was sparse attention to some plots that I previously liked (such as Arya Stark). There was quite a lot of attention to other plots that I had no interest in (the iron men/Greyjoys and Dorne). And one plot that I previously liked just circled around (Brienne of Tarth) without doing much at all.
A story with so many viewpoints is difficult to keep moving. I have not decided what I think about the tradeoffs that one has to make to write such a novel. On one hand, the novel can be richly textured. On the other hand, each story moves slowly because of the alternation between characters.
Perhaps one day I'll find a story that I know would best be told by alternating so many viewpoints. But for now, I prefer the smooth, fast moving single viewpoint story.