Euron is probably the most vile character in the book
I agree.
I love the way the ‘principal evil fucker’ character started badly with Joffrey the cunt, then got steadily worse when Ramsay took up the mantle and now Euron’s poised to up the ante yet again. He is one demonic bastard.
I also love the way George obviously wanted to read The Forsaken chapter for years and was always offering it up at comic con and the like, only for the fans to reject it because Aeron is a boring dweeb. When it finally got out, we all realised what we’d been missing. 
In terms of the ending, I think D&D have been given the broad brush strokes, but their execution is/will be just so much more pedestrian than George’s. Take Sansa. I just know that George’s version of Sansa fucking over Littlefinger will be so much more nuanced, unexpected and powerful than what we got dished up last season.
Not to mention all the storylines that haven’t made it into the show. I’m still pissed that they left out Arianne. I love Arianne. Pet theory alert, but I’m convinced that in the books Arianne will marry young Griff, newly crowned king of Westeros, and at their wedding we’ll get the wildfire revenge plot from Cersei that the show dished out to the Tyrell’s. The green wedding if you will.
Not that it’ll happen probably. Sigh.