I think the second half of season 4 should be pretty decent, as long as they're not in one place too long. It seemed like season 3 was kind of lethargic by the end. Having to spend half of season 4 at the prison wasn't great either, but the little interlude with the Governor helped break it up. I think the show does better when the cast is on the run with a horde of zombies at their back and obstacles in front of them along the way. Theres more action, less constant talking. I still love the show, and I watch little TV these days so I don't really have any great shows to compare to, but that's my opinion. Loved season one and most of season two, like where they're going at the mid season finale in four here.
I'd like to see some more borderline characters to add some diversity to the cast. Some chaotic neutral guys like Merle, someone who doesn't like to follow the rules, but isn't necessarily always leaning towards the bad or the good. It seems like we've got a lot of good guys that follow the same patterns: Glen, Maggie, Rick (Although he's flakey at times), Hershel (RIP), Darryl, Beth, etc. Tyreese is good, but he's been pushed a few times and could bring an interesting dynamic. Carol was just getting interesting as a character before she was dismissed, hated her before that little transformation. Shane obviously had an interesting stance, but there was no way he was going to survive the way he was going. Actually, they should just bring Merle back from the dead, that would work for me.