There are so many parts of this series that are outstanding, that catching them all would take too long and wouldn't help anyone reading it because the only thing that that would lead to is spoiler content. Thus, I'm making it very short: At the start I believed the still flashy, but not as bright excellence of season 3 would continue but luckily it proved me all wrong. I only have one sentence to describe this season and I think many will think the same:
This series will never cease to impress me.
FU2016.
Edit to fill the lines: I'm not an American, nor do I really care about their politics. But watching them dig their own grave by having not one presidential candidate that radiates strength really troubles me after just watching this series. Finish it and ask yourself, if any of the current candidates would make a good standing at just one of the troubles that occur in this fictional, but at least somewhat realistic series.