According to the author, books 4 and 5 in the series were actually supposed to be one book—and they basically are one book in that they take place over the same period of time, but the story is divided into what’s going on in Westeros (book 4) and what’s going on outside of Westeros and in the north of Westeros (book 5), essentially two stories running in parallel. There may be a bit of overlap, but that’s the gist. In other words, by this point in the story, there are so many subplots and characters that they could not fit into one 1,000 page book.
If I were Martin’s editor, I’d say “Ummm…it’s time to cut. If you need 1,000 pages just to develop the story for half of your characters, you have too much going on.” The result for me is that I’m done. I enjoyed books 1-3, but I’m only interested in about half of the characters at this point which means I’m skimming pages of plot about the ones I’ve lost interest in (or the ones in which the subplots have so many sub subplots and characters that I’ve lost track of what’s going on). And for most of book five, we just have to “hold on” to everything that happened in book 4 because none of those folks are in book 5—-other than a few mentions, it’s like they dropped out of the story.
We have to wait till the end of book 5 when the story sort of merges again, attempting to rein in the various plot tentacles. Not only did I lose track and interest, I found the overarching theme of “I-am-the-true-heir-to-the-iron-throne-and-must-seize-it” a little too close to our current president. I can’t read about power mongers in a book and then read essentially the same thing in the daily newspaper. I slogged through book 5 in August (yes, three months ago). Maybe I’ll try book 6 next summer (if it ever comes out), or maybe I’ll break down and watch it all on HBO.