Based on A Song of Ice and Fire series of novels. The first novel was called A Game of Thrones.
Sean Bean as Eddard "Ned" Stark, Lord and Warden of the North
Michelle Fairley as Catelyn Stark, wife of Eddard Stark
Richard Madden as Robb Stark, the eldest heir of House Stark
Sophie Turner as Sansa Stark, the eldest daughter
Maisie Williams as Arya Stark, the younger daughter
Isaac Hempstead-Wright as Brandon "Bran" Stark, the middle son
Rickon Stark is the youngest son with no lines in the first few episodes
Kit Harington as Jon Snow, supposedly the illegitimate son of Eddard Stark and a woman, Wylla
Mark Addy as King Robert Baratheon
Lena Headey as Cersei Lannister, the Queen
Jason Momoa as Khal Drogo, warlord of the Dothraki
Some people might recognize some names. Sean Bean from Lord of the Rings, Mark Addy from the Full Monty, Lena Headey from 300 and Terminator: The Sarah Connor Chronicles and Jason Momoa from Stargate Atlantis (as Ronon Dex).
I was impressed with the awesome landscape and cinema photography. The story is very driven by the characters, drama and brutal reality of the time period. Any fan of medieval fantasy should at least watch the first 3 episodes. The third episode isn't up yet but I have to watch it. I haven't read the books but I'm intrigued by this whole concept.