I agree with Mark that this is probably the best sci-fi show on TV right now, maybe ever. The writing and character development have been getting stronger each season, which is a significant achievement.
In addition to the no-nonsense Earth leader (played by Iranian-American actress Shohreh Aghdashloo), who gives more nuance to the F-word than anyone this side of The Wire, I also liked David Strathairn as the crusty old space commander. Apparently Strathairn’s character was a villain in the book, but his character has evolved more nuance here, largely as a result of the positive response from viewers. Fan service isn’t always a bad thing.
The show also has a quirky sense of humor, beginning with the police detective who always wears a hat even though he lives on a space station. This year, you had a character animating a piece of old space junk to do battle with an evil alien. It was the climax of this year’s storyline, but it was also just nuts.
A great show, but start from the beginning. Although each season has a distinct plot line, they are always referring back to things in earlier seasons.