It has a lot of great parts, but a lot of it could have been trimmed. Seriously.
The Martells are great. Nothing to argue about here.
The Greyjoys... sorta. Their plot is good, but it's hurt by the fact every Greyjoy except for maybe Euron and Asha is incredibly. fucking. stupid. Seriously. I'm praying Victarion's fleet is eaten by a kraken or something and Aeron drowns for the final time, so maybe we are forced to have Euron as a POV character.
Cersei ranges from excellent to meh. "Excellent" because Martin is really good at political plotlines, "meh" because of how unlikable Cersei can be.
Jaime is the best part of the book. Nothing to complain here. He has become my favorite character in the series after Tyrion.
But Brienne is the worst. While I like her character, I feel like 2/3 of her pages could have been cut off and the book would have only improved. It ends on a cool cliffhanger, but otherwise it's just a bunch of pointless traveling.
Samwell is average. The character is likable, the plot is mostly boring. Though it ends on a high note.
Arya ranges from "this is fucking awesome" to "what the hell did I just read". But that's what Arya has aleays been about. Nothing much to say.
Sansa was the pleasant surprise of the book. This is the best she has been in the series, having matured and finally being in a place where the universe is not trying to make her suffer. Also Littlefinger FTW.
So yeah, the book had highs and lows, and a lot of parts that made me stop and not come back for at least a week. Namely every time the word "Brienne" appeared on the top of a page. But it started getting really good towards the end. I think I read the last 200 pages in like 3 days. Love seeing Cersei suffer for a change.
I think the decision of cutting book 4 in two separate books was a bad one. We could have had a book slightly longer than book 5, and with a lot less filler.