They have only been at the farm for 6 episodes, so they can't develop every character on the show all at once. I listed all the characters that have been developed so far as well as introducing new characters (Herschel and Maggie). I think Dale and Lori are going to be pushed to the forefront in these next 5 episodes.
T-Dog, well, he is probably zombie food at some point so I don't ever see him being a fully developed character.
I made the ADD comment and I stand by it. To repeat, they've only been at the farm for six episodes to date. Six. 6.
While the premise of the show isn't exactly realistic, the actions and development of the characters in response to this premise needs to be and is. I wouldn't find this show nearly as interesting and thought provoking if it was a "run and fight" zombie battle of the week, rinse and repeat format.
Don't know how many people are complaining about the show, but viewership keeps on going up (latest episode drew over 8 million viewers!) so they must be doing something right.