First of all, I must say that I enjoy the TV series. However, I believe that AMC took some of the fan favorites from the comic and completely botched them on the show.
First of all, Andrea. In the comic, she was a relatable person who added SO MUCH to the story, having believable relationships with core characters like Dale and Rick. But in the TV show, she is one of the most unlikable characters I have ever seen. At the end of S1, she wants to die. I get that. But a couple episodes later, she's fine. Also, she doesn't listen to the other characters, such as when she shot Daryl (after she mistook him for a walker) despite Rick directly telling her to hold her fire.
Secondly, Michonne. In the comic, she is basically the most awesome character. Everyone's favorite. But in the show, she shows so little emotion that she is not a believable character. In Season 3, she almost never smiles, and spends most of the time being the stereotypical "angry black woman". Her only redeeming acton is how she gradually builds character.
All in all, I think that AMC made a HUGE mistake in taking these characters in the direction they chose.