I used to think people were being melodramatic when they would say George R.R. Martin isn't ever going to finish the book series, but in the past year I've come around to believing that myself.
It's been what.. 13 years since the last one was published? And apparently in his most recent blog update on the progress he was about 2/3 done with Winds of Winter, unchanged from the year before. It's too bad. This could have gone down as the greatest fantasy series of all time, overtaking Lord of the Rings for that title, but it's always going to be looked at as a disappointment by fans.
P.S. The book series Memory, Sorrow, and Thorn by Tad Williams was GRRM's inspiration for A Song of Ice and Fire. I haven't ready the series yet, but it supposed to be really good, and another thing it has going for it.... It's completely finished!