The first season with its 12 episodes is based upon the life of a CIA office Carrie Mathison and a US marine Nicholas Brody who was held captive as a POW by Al Qaeda. Brody returns home as a hero to his hot wife who by that time had believed that he was dead and had conveniently cheated upon him. However, people respect him as a hero who was tortured badly by the enemy but still managed to stay alive, while Carrie suspects that there is something fishy about this heroic return.
The show revolves around the two mainly with a couple of other characters coming into picture. The show will take you on a journey of twists and turns and just when you will start to believe that you know what's going to happen next, there will be a new turn in the story. There are no long stretches of boredom and you would always want to know what will happen next.
I personally am waiting for the next season which will come this September. The show has received a lot of critical acclaim and is IMDB 8.6 which I think is a bit harsh. A must must watch, is what I'd say.