Green Ronin's role playing system for A Song of Ice and Fire has a lot that sets it apart from other roleplaying games and really lends well to the imagery and world that George R. R. Martin has set up.
I won't go into what makes the setting itself so appealing since that type of information is available else and related much more elegantly than I could phrase it. Here I would like to highlight the strong points of what I feel to be a very rich and logical roleplaying system.
My roleplaying game of choice has always been D&D, so I will use this as a basis of comparison. Instead of 6 core abilities and a multitude of related skills, GR combines these concepts and sets up 19 abilities. An average score is 2, but could range up to 7. There are no classes in GR, but rather the player assigns experience points to abilities or specialties to form the character as he sees fit, rather than getting a lump package of improvements per level.
You "test" a skill by rolling a number of 6-sided dice equal to your ability. Every test has a difficulty assigned by the Narrator. Most basic actions have preset difficulties, but they can always be adjusted as circumstance (or the Narrator) dictates. If the total rolled on the test dice meet or beat the difficulty the character succeeds. The use of skills, combat, and even intrigue are all handled using this same concept.
In D&D there was nothing half so frustrating as having a huge attack roll only to follow up with minimal damage. That situation is mitigated with the GR system. The greater your attack roll, the more damage inflicted.
With so few abilities in D&D it was easy to buff up one or two to really excel at combat. This isn't an issue in the GR system. In combat the difficulty of your attack is your opponent's Combat Defense (similar to AC). This is basically number derived from various abilities (Agility + Awareness + Athletics). That means multiple abilities become important to avoid getting hit besides just one (as with Dexterity in D&D). Testing the Fighting ability is typically used for melee combat, but damage is usually dependant of Athletics (rather than both relying on Strength as in D&D).
The players have much more control over what happens to their characters in combat. D&D would have some situations where characters could get killed quite easily before their player could react. GR introduces injuries and wounds to give more control back to the player. While characters have relatively low Health scores (hit points), whenever they receive damage the player decides to accept the damage or take an injury to lower the damage sustain a small amount, but then suffer a small penalty for the injury until healed. Additionally, players could choose to take a wound to remove all damage sustained from the attack, but then suffer a much larger penalty. Also, wounds can take a long time to heal. If a character is reduced to zero Health the person who defeated them chooses their fate (unconsciousness, maiming, or most commonly death). Basically, the staving off of instant death gives much more opportunity for retreat or surrender rather than death.
The game system also introduces a system for creating a house to which the characters can belong. Houses can act as a pseudo character that is shared by all of the players. Sometimes characters can use house attributes to improve their standing. Sometimes the characters can invest personal rewards into the house to increase its standing in the world. And isn't that what playing A Game of Thrones is all about?
Green Ronin offers a free downloadable quick start rules to give a better understanding of the game mechanics. I highly recommend this system and hope it sells well so that future products are produced.