1. All Out War
The Walking Dead found its success as a character drama that was set in the aftermath of the zombie apocalypse. These characters dealt with emotional trauma, searched for their families, and the things that were important to them while the world around them fell apart and the dead roamed the streets. The All Out War arc has turned into a weird version of a second rate shooter game, with entire episodes devoted to running gun battles through various locations. There is no character development, and the drama isn't generated within the characters, but between arbitrary groups all trying to kill each other and not be killed. People aren't engaging with the new story arc because its not why they watched to begin with. It is like watching a cooking competition show turn into a war documentary in the last act.
Solution - wrap up the All Out War arc, and turn the show back into a drama that had random moments of violence, or a single episode based around action. Also, pay attention to the audience, and know what the audience wants.
2. Card Carrying Villains
The big villain in the current arc is Negan, and his lackeys Dwight and Simon. They are trope card carrying villains, bombastic, interrupting, cheesy, and full of undeserved swagger. I suppose they are supposed to be so confident that they are jovially evil, the sort of monster that asks for lemonade before killing the residents of a house. This renders them one dimensional, disinteresting, and ultimately unsympathetic. Previous villains, and good villains, have strong justifications for their actions, and when you see their side, their story, it makes sense, and there is a sense of sympathy. The Governor was a profoundly broken man who had created his own make-believe version of life after the undead. Negan is unsympathetic, and ultimately, Jeffrey Dean Morgan's charisma aside, boring.
Solution - Better villains, who are less cheesy, and who have better motivations than 'to be the villain'. They have their own arc in which they are the hero.
3. Life and Death Stakes
The show has not shied away from killing characters in dramatic fashion, and entire groups can be wiped out across a season, such as the Greene family, the prison inmates, etc. The current arc has seen the execs of the show generate interest and attempt to keep flagging ratings up playing the WHO WILL WE KILL THIS WEEK, putting fan favorite characters in mortal peril and killing them for the pathos and ratings. This is in contrast to previous character deaths that were emotionally devastating. The current character 'assassinations' are cheap.
Solution - don't cheap shot kill characters, unless it is the service of Advancing the Story. Not for ratings, not to generate internet buzz, and not to lord over the fans.
There are several characters who are now increasingly prone to long monologs. Negan is an egregious offender with long bombastic threat filled tirades to mute audiences of bound characters. They are stand ins for us, the audience, who are likewise powerless to do anything but sit and listen. Rick and several other characters are prone to long one sided speeches. The rare speech, before a battle, or after a loss is acceptable. More than half an episode devoted to a long winded speech, ugh.
Solution - one of the most basic instructions in creative writing is Show, Dont Tell. Replace long monologues with scenes with characters interacting, and doing things. The monologue is the character version of an info dump.
5. Too Many Character Arcs
Something that seems to be increasingly afflicted fiction, rather than telling a small number of character arcs within a greater story arc, the Walking Dead is chasing too many loose ends. The important parts of the story are spread out further and further as the narrative tries to keep up with characters who are scattered across a map and moving dynamically within the flow of the story. Instead of weaving a cloth, it is a snarled tangle.
Solution - not every character needs their own side arc. Those arcs that don't serve the greater story can be cut.
6. The Walkers
One of the early aspects of the show that drew in viewers was how good the zombies looked, and how much of a threat they were. A single walker could be a serious threat, and some of the early series walkers are very recognizable. In the current state of the show, the walkers are just a distant threat, no big deal, the one terrifying herds are redirected, they are used like weapons, and get much less screen time. The only threat that the dead present currently is being a Jack In the Box surprise to deliver a character killing bite, or when a bitten hero dies and turns into a sweaty milky contact wearing version of themselves. The dead are not the threat, and this has taken the point of the show away from the context of mortality and the death spiral of humanity. As a counterpoint, in previous seasons, the survivors keep shrinking in number as they struggle through post civilization, with occasional reinforcements by absorbing other groups of survivors. The Saviors, in contrast, seem to have an endless supply of goons, guns, food, and ammo. No one is hungry, no one is running out of bullets, they always have the numerical advantage. Rather than feeling like a serious threat, they feel like facing off against a DM who isnt really well prepared so keeps pilling up foes for the heroes to fight so they are constantly reminded that they are at the DM's mercy.
Solution - this one is more difficult, because with experience, the walkers are less of a threat, but they shouldn't be gone from the show to the extent they are now. More 'hero' walkers can help this.
7. 7th Grade Writing
Many of the above problems can be attributed to just bad writing. Mid-season episodes end on cheap cliffhangers, characters have no depth or interest, bad dialog, long monologues, confrontational scenes that feel more like mini-game decisions wedged into an overly long cutscene from a game.
Solution - Fire Scott Gimple