A few random thoughts I had along the way:
Arya and Sansa getting the news of Jon's parentage would have happened on screen!
The twists and turns of Varys' storyline would have continued throughout the seasons, rather than turn into somewhat of a magic act complete with the ability to suddenly appear and disappear rather randomly, before suddenly going up in flames on a beach with virtually no build up to actually make it resonate deeply as it should -- particularly where the endgame was headed.
The Night King's fascination with Jon at Hardhome should have been explained. It's clear it wasn't forgotten by the writers because we once again got a scene with the NK pausing to take in Jon's presence in particular, before once again stretching out his arms to raise more dead soldiers. We also don't know what it was that made him pursue Bran.
The molten Iron Throne should have flowed over Danaerys' body, poetically encapsulating her quest for eternity and creating a strange and distorted echo of both her father's and brother's fates. The fact the dragons recognized Jon as a Targaryen should have caused comments and discussions.
Sansa should have become ruler of Westeros, with Jon as King of the independent North. Bran could have served as advisor to both. Part of Tyrion's duties as hand to the queen would be overseeing the care of Drogon, who would not care to live in the cold northern climate with Jon. He would also manage the care of dragon eggs Arya would bring back from her travels, seeing to it that they were safely hatched. Brienne would be head of the Queensguard -- and NOT have slept with Jamie.
More focus on characters and decent dialogue over EPIC battles, and greatly diminish use of CGI. All these years of getting attached to the characters and most of the tremendous character development and the acting performances were wasted by the writing of the last two seasons in particular.