3. Andrea's Death
I certainly have my issues with the way Andrea's death was handled - and I'll get to that in a minute - but in terms of the dramatic heft of the scene(s) in which Andrea was locked up with a dying Milton, it finally put to rest a character who has had one of the most intriguing existential struggles throughout the show. In Season 1, she was bent on suicide, and she continued to wrestle with that in Season 3; now she's finally got what she wants, and her character is at peace. Many have criticised the character for not being very likeable nor particularly well-acted, and though I agree that she's not very likeable, I have to commend Laurie Holden for her work on this episode. She did the best she could to give her character an emotionally satisfying payoff even if most people probably weren't that sad to see her go (the writing has been on the wall for a long, long time). One of the better-developed character arcs of the show's entirety came to an end in a suitably intense fashion.