I've been watching The Walking Dead regularly since 2012. I found the first season one of the best because everything was novel and the show seemed very well written.
The second season was more slow-paced that the first one but still interesting. Lots of new characters were introduced including Hershel and his daughters one of whom is still one of the main characters in the show.
The prison seasons were great. Although the Governor wasn't as dark in the television show as in the comics, he was still a seriously disturbed and well-portrayed character. The Governor was a lot like I imagine a lot of top politicians are like in countries where the rule of law is weak and the power struggle a mortal danger to those involved. A good guy on the surface but with a ruthless and Machiavellian side.
Negan has probably been the most engaging bad guy in the show so far despite not being one of the bad guys any longer. During Negan's reign, it was impossible not to dislike him. I read somewhere that Negan was a gym teacher before the zombie apocalypse, a nasty one you wouldn't want to mess with. Interestingly, his particular brand of tyranny had a strong pedagogical element to it. He'd always avoid killing people if possible considering that to be "wasteful" and opting for crushing their spirits and making them his servants instead.
After the downfall of Negan came the Whisperer war. That particular tribe was a little over the top in my opinion. The crude, crass and condescending Negan was a perfect counterpoint to their bullshit philosophy. It was satisfying to see their leader being cut down by Negan in the end.
After the early seasons I've been forgetting to tune in when TWD is on much more frequently. I think it has to do with the fact that there have been episodes where nothing much happens and where the characters keep having "deep" conversations that sound like ones no one has in real life. That's poor writing and prone to putting the viewer to sleep.
The Walking Dead is pure entertainment, of course, and the skillful portrayal of characters is not really one of its strengths. All sorts of tragic events take place and the people react to them like you would imagine people react but that's pretty much it. At best, the plot twists and scenes can be riveting.
But character development isn't usually very believable. For instance, let's start with Carol. Her character development takes her from a timid housewife under the thumb of her controlling and abusive husband Ed to a bad ass fighter and stone cold killer when necessary. I think it was in the fifth season when she, shall we say, euthanizes an otherwise healthy ten-year old girl who suffers from a dangerous delusion that the walkers are not dangerous at all and who put her little sister in grave danger because of that - by shooting her in the back of her head from a distance. There is no continuity between Carol in the first season before Ed dies and her in the rest of the series. If she had all that in her, then I don't think her maternal instincts would've allowed Ed to continue tormenting her and making her and their daughter's life misery by abusing her/them.
Another case is Merle, Daryl's brother. Merle is a complete scumbag until he has a sudden change of heart before dying a heroic and altruistic death in the hands of the Governor. If Merle was motivated to improve himself, that should've been introduced earlier in the show thus making his sacrifice a logical conclusion of a more drawn out and gradual change. Another character whose redemption is an interesting and somewhat questionable case is Negan. After Negan was defeated, the Alexandrians put him into a cell in a basement instead of executing him. Negan finds his rock bottom moment in the cell. When he's finally let out after many years, left without a group to lead and despised and hated by a lot of the people in the group, he decides to work towards getting on their good side, which he's somewhat successful at by becoming an undercover agent among the Whisperers on his own initiative and killing their leader. It will be interesting what the writers will make of the ongoing relationship between Negan and the Alexandrians. Unlike Merle, Negan is quite intelligent and also has a very flexible and pragmatic mindset. Maybe what he's doing now is basically just what he thinks is the best way forward for himself at this moment. Also, he's not a complete asshole because he has genuine affinity for some children such as Judith.
I think The Walking Dead should cut down on the chatter and stick to plot building and the action. The show has always been at its best when there is an element of mystery or a series of predicaments the main characters must get through. Most of the characters are far less interesting than the world they find themselves in. What the show has successfully portrayed are the signs of decay in what's left over from civilization. No one drives cars any longer. Daryl's motor cycle is the only motor vehicle I've seen on it for a while. The walkers are much more decayed at this point than in the beginning.
One element that has been conspicuously lacking in the show from the very beginning is humor. That is a serious flaw. Negan is the only character in the habit of cracking jokes but they were never good. People make jokes in any situation to lighten up the mood. Humor has potential to add to the quality the dialogue. The genre is not comedy and humor should not be overdone in this case but I find it odd that there is almost none of it in the entire show.