I think that the criticism of slowness is being conflated with a lack of physical action. Maybe that's accurate for some criticisms, but not all. Slowness can also mean a lack of character development and a lack of plot movement. I think that's the most accurate criticism.
Let's take the ongoing Sansa suffering as an example. Compare her being shown her father's head with her rape. IIRC, they're about the same length. In the first scene, Joffrey's cruelty is taken to new heights, and I think there is a pretty important interaction between her and the Hound. On top of it, we see her stare at her father's head and deepen her hate of Joffrey. In the second, Ramsay asks about something we know and rapes her. Given the characters and the circumstances, it is expected. Reek's watching turns out to ve inconsequential so far. To add insult to injury, the Darth Sansa that people were raving about is apparently nonexistent. We may have seen it in her conversation with Ramsay last season, but it basically recapped his conversation with Roose and she didn't plant any seeds of discord, so whatever. Less character growth in the later scene.
We could also take Dany's power growth over the last several seasons. She went from an object to be sold, to the Khaleesi, to the mother of dragons, to the mother, to the breaker of chains or whatever, to being an incompetent ruler of a slave city. This season has seen her in the last role without change, with what we must assume is a diminished power base, but it is unclear whether she's in danger of being driven out of the city yet. No real growth in her.
If the game of thrones is about shifting power of houses, I'd argue that the majority of pieces have been static this season, with the exception of Tyrell, Lannister, and the Faith Militant - and even then those pieces have only moved in the last two episodes.
So, I don't need to see Tyrion ride a dragon to defeat the white walkers to be happy. I do need to be given more reason to care about those houses and those that belong to them and see them at least plan to make moves rather than have gratuitous sex scenes, Xena girl power clones, and gore with some magic and lore thrown in. Therein lies the path that True Blood walked and the road to ruin.