One of the distinctive things about George Martin's world was the prominence of clever schemers. Much of the action in the books was dominated, not by the big guys with swords, but by backstage operators like Littlefinger and Varys the Spider. Even Tywin Lannister seemed to accomplish more by treachery than battle. When Robb Stark was a successful fighter it was by trickery as much as by courage. The best character was the smartest, the dwarf Tryion.
Once the TV show outran the books, all that fell away. Jon Snow's apparent imbecility has become a meme, and after Tryion went two whole seasons without having a single good idea the other characters started mocking him for it. Which was amusing, but a poor substitute for characters actually doing smart, interesting things.
Various writers have offered theories online about why the showrunners "abandoned the smart characters," you know, something about giving up on plot and just going to dragons and fireballs and other easy stunts.
The real reason, I think, that the show stopped having clever tricks or brilliant stratagems is that the writers couldn't think of any. It is hard to come up with clever plots or stunning battlefield maneuvers. A brilliantly sinister ploy like the one Littlefinger nearly pulled off is just hard to imagine; of all the fantasy authors I have ever read, none have close to Martin in this department. As commenter Observer29830 put it on Youtube:
First rule of writing fiction: You cannot write a character that is smarter than yourself. And the authors of the last season are not particularly stellar.(Not that the Game of Thrones writers are unique in this; their battles are works of genius compared to the Imperial Bungling at Hoth.)
As I have watched the final season with my children I have continually pointed out better strategies all the commanders could have used in battle, to the point that my children have started to telling me to write my own damn series.