Not only is the production quality of the show outstanding but so is the cast. There are few actors in the series that i recognize from other films however after every episode i am blown away by all of them. And there is a lot of them. The show is extremely deep and follows countless characters, and storylines.
On top of that there are Dragons... Who doesn't like watching shows that have giant man eating winged lizards? The CGI is another aspect of the show that is phenomenal. However, the CGI of the dragons is so expensive that the show can only have them on for a limited amount of screen time. Animations can really rack up the bills fast, however I am glad that they dont over due the dragons so in the long run I'm happy with it.
If you haven't started watching Game Of Thrones I highly recommend that you start. It will take you by surprise.