The 3 things that bothered me greatly about Game of Thrones TV Show is the recasting of The Mountain and Daario Naharis, as well as the way they portrayed the Red Viper in the show.
Firstly, The Mountain now looks like a big baby worldwide wrestler instead of an intimidating, menacing, weathered-looking warrior. He even looks younger than The Hound - who's supposed to be his younger brother. In short, the TV show made a jester out of The Mountain.
I can't really remember who I had in mind for The Mountain when I first read the books years ago, but I certainly didn't picture him looking like this new actor they casted for this role. If anything, The Mountain should look medieval, unkempt and animalistic.
Loved the first Daario, the second... total disappointment! Daario is supposed to be wild and an interesting looking guy who stands out in a crowd. The new Daario fades in the background and could be mistaken as one of the extras. Ed Skrein was perfect for the role and he had great chemistry with Emilia Clarke, it's a real shame they decided to change the actor!
When I read the books, I pictured the Red Viper as The Rock (Dwayne Johnson). The actor who played it on the TV show did well - the main thing that I didn't approve of was how they focused on his sexuality rather than his roguish mystique. His first appearance should've created a mysterious and even legendary aura instead of proclaiming that this dude is gay/bisexual/whatever. Total turn off! Otherwise, I grew to like the actor as Oberyn.