who's character development? the only character they went away from was Jamie boinking Brienne which was the 1 time they went for pure fan service and I thought it was betraying how he loved his twincest ..
Jaime - His entire redemption story was ruined. They spent several seasons humanizing him, making him care about things other than just himself and Cersei. Then Cersei hires a hitman to kill both Tyrion and Jaime and Jaime decides to go to King's Landing and
SAVE Cersei? GTFO with that terrible writing, who on this planet is going to go sacrifice their life for someone who just hired a hitman to kill you? You could say he was going to save his unborn child, but it has been made pretty clear that Jamie doesn't actually care about his offspring, just Cersei and himself.
Tyrion - His whole shtick was drinking things and knowing things. Except what exactly has he known in the last few seasons? He trusted his damn sister, and kept commenting on how she wasn't a monster...
AFTER she hired Bronn to kill both he and his brother. Horrible writing again. He also advised Dany to not go straight to Kings landing, which she could have taken with minimal civilian casualties had she not gone north and lost her damn mind. He has made almost nothing but stupid decisions since arriving back on Westeros. Tyrion has turned into a guy that doesn't drink all that much and doesn't know shit.
Euron - His character development never even started. He's like a less drunk Jack Sparrow who is obsessed with sex. Book Euron is a waaaaay more interesting character.
Varys - The dude who had few equals when it came to spying and scheming betrays his Queen directly in front of her Hand by asking the dude she has been banging recently to betray her... what?
Dany - Her decent into madness was just poorly handled. Shes has been sold as sex slave by her brother, had her husband die, had her unborn child die, led her starving followers through the Dothraki sea, had two of her dragons killed (one of which was resurrected and fought against her) and been betrayed by people closer to her than Varys already. All of that happened, and she still wanted to free the oppressed and "break the wheel". But Missandei being killed, Varys' betrayal and Jon telling his damn family who his real parents are were all it took for her to snap and start burning the innocent alive? That is weak.
White walkers - Died to a freaking sneak attack. Ayra killing one would have been fine with me, but her just materializing behind the Night King and just "knowing" that she had to stab him directly where the Children of the Forest inserted the dragonglass into his chest was just poor story telling. HOW did Ayra sneak in there? HOW did she know she had to stab him in that specific spot (D&D said that she knew)? Way too much dues ex machina.
I'm sure there is more, but these are the main ones that pop out to me. Of course you can hand wave this stuff away, but all of these characters could have ended up meeting the same fate in a way that made more sense.