There are many key episodes in the season. The first episode of the season 1 is definitely an important one. Then of course, the twisty episodes such as now his watch has ended from season 3 is also important. Unbowed, unbent and unbroken is another important episode for viewers. In short, many episodes contain vital keys of the plot and cannot be missed.
We recommend that you watch the entire season so that you understand the whole story completely. Otherwise, you may not know the background of many characters, especially as the finale will end up concluding everything from the first to the last season.
There are several essential episodes of Game of Thones especially for people out there who are first being exposed to the series. Obviously the first essential episode would be the very first one from season one. It is in this episode where viewers are shown four of the warring clans that later on would become essential to the plot and layout of the show.
And Now His Watch has ended from Season 3 is very essential and one that the writers and producers of the show is one of the most important of the series. The change in command of the Night's watch sets up for some very interesting happenings in the course of the show. Unbowed, Unbent, and Unbroken from Season 5 was one episode that was said to have veered off from the inspirational books and novels.
This was another episode that showed the brutality and sadistic nature of certain charchters. There are plenty of essential episodes in Game of Thrones. For a person who has never seen the series or watched during its initial run, the best thing to do is start from the beginning and watch.