The difference is in the writing but more specifically in the direction that the characters are the focus, not the events that happen to these characters. This sounds simple but it is very effective thing that the show does because it means you engage with the character and, by and large, go with them through whatever they go through – not because the specific event is the thing that does it. This shows a great deal in this season because, as I said, some of the detail here isn't totally convincing if you laid it out as just simple statements. It isn't laid out this way though, it is laid out in the context of flawed people going through their specific life, whether it be the temptation to cheat, the inability to communicate with someone or just day to day tensions caused by the clash of personalities. This is very convincing and the characters feel very real so that even when the plot developments are perhaps not so "day to day", I never struggled to go with it, because within the them the characters and their reactions just worked.
This also helps some of the observations made in the writing, some of the "truths", because rather than being pat or smug, they are backed up by those going through the subject – so these lines of dialogues and scenes work because again we buy the characters, have seen how they got there and it feels genuine. Again, very good writing. The cast continue to deliver on this potential. Krause has some of the harder material due to its excess but he mostly makes it work and the actions of the character are sold by how well he gets his role. Hall is the same and convinces whether he is under extreme trauma or if he is just having spat with Keith. Conroy continues to be great while Ambrose is allowed to grow up and herself become more and more of a person and again she makes the most of this. Support from Rodriguez, Patrick, Cromwell, Griffiths is consistently good – although I should not say support since they are all brought to the fore and make up a stronger front than before.
The third season was very much about lots of relationship problems and things falling apart and, while season 4 is still dark and full of conflict and trouble, it mixes it up more to include love, humor and human touches in a way that enhances the darker material by way of placing it within a much more familiar world. It works very well, allows the characters to develop and be flawed and generally makes for an emotionally engaging season.