So I've binge watched all 5 seasons starting in January when my wife took up night classes and my son went to bed. I finished up season 5 last night, which conveniently coincided with my wife's finals. I'm caught up on the show, but not the fan theorizing, and haven't ever read the comics so if my thoughts aren't original I'd like to be clear that I'm not making any claim to that.
Anyway, I think there's an interesting underlying conflict in this show revolving around how the individual influences society, and how the society influences the individual.
By this I mean, it is clear that Rick Grimes is a product of his environment. His behavior has changed in response to the greater conditions around him. However, Rick is also a pivotal figure in shaping those conditions - his presence changes the dynamics of every new group he encounters.
The more I think about it though, I don't think Rick is on a hero's journey. I think he's actually on a villain's journey. The characters talk a lot on the show about the line between a good person and a bad person, and that in their current world good people often resort to bad things so it's harder to tell them apart. Rick doesn't stand completely outside of moral ambiguity, but I don't think he can be defined by being good or bad, he's just defined by what he is - a conqueror. Every group he's encountered (has been destroyed, with a handful becoming part of the constellation around him. The mortality rate around Rick ain't good though. It's not clear if death is just a consequence of the state of the world they're in, or if Rick brings death wherever he goes.
I think Rick's a sympathetic bad guy.