I watched the series again from season 1. I agree, first two seasons were awesome. It's because the situation was new to us.
As the series progressed, they had mastered dealing with the walkers. So much so, they had become a backdrop for other plot lines.
Watching the series again, characters and some details made some things clearer for me. I also revisited the relationships of people and their character development.
Season 5 Episode 9 showed the beginning of Glenn's transformation. While the action was relatively slow, the show needed to breathe and show the character's thoughts and feelings. It cannot be about zombies or wars all the time. Think of it as a scripted reality tv show.