For people who haven't read the books, you have no idea the kind of awesome that is coming.
The tv series does the books proud, every character (except maybe Cersei for me) has the perfect actor. Especially Arya and Tyrion.
Robert Baratheon was the best for me. He portrayed the once heroic war hero, now fat, lazy king to absolute perfection. Several of the best dialog scenes involved Robert, the one with Jamie and Ser Barristan talking about their first kills in particular.
I do agree that they really hit it out of the park with the actors, the child actors were incredible, every single one of them. Joffrey was a sly little bastard, Arya extremely loveable, Bran was good and Sansa showed a lot of promise towards the end of season 1.
Every single Lannister worked for me, Tywin, Jamie and obviously Tyrion in particular. Robb was great, Ned... hell they are all fantastic. Amazing casting.
The only one I absolutely hated was Ser Loras Tyrell, The Knight of Flowers. Without spoiling to much I'll just say they are gonna have a lot of work to do to bring some credibility back to his character.