I was focusing on these two because the books always describe them as very close to each other (Cersei even envies them for looking more alike then she and Jaime), whereas we see very little of Garlan and Willis.
Loras is the perfect bishonen here. Almost like he came out of a Yoshitaka Amana painting, minus pretty flowing things in background, but everything else about the character design is nearly spot on to that style.
But Margaery had dark brown hair and big brown eyes, not red hair and blue eyes. The art is beautiful, but her coloring is all wrong. I particularly love the dress, especially the detailed blue flowers.