Ser Barristan does not recall serving under an honorable king so that means no serving under Jaehaerys II

Ser Barristan did not sit upon the small council though he did in the books (this is changed, for in the books he purposefully hid his true identity until Season 4 for he wanted to see if Daenerys is tainted, if he sat upon the small council he would instantly denounce Mormont).

The Unsullied in the books get a new name each day, always vermin though, grey work considers his name lucky for he had this name on the day he met Daenerys Stormborn.

Karstarks were not half Robs army in the books. 300 cavalry and 2,000 infantry. The cavalry for sure left but it was not made clear on the infantry. They also downplayed the size of the Tyrell army.

They got rid of Lora's older brothers in the show, making Loras the heir. Furthermore Loras was obsessed with Renly in the books and would not take another lover after Renly died, instead choosing celibacy.

Cersei in the books was given the choice of husbands Balon Greyjoy (an old man who was still married), Willas Tyrell (Loras older brother, a crippled but heir to Highgharden), The Red Viper (Pure Awesome, but a hothead lustful man who Cersei would see as a second Robert, someone she couldn't control who was controlled by his urges).

We still haven't seen Kevan Lannister since Season 1