While it's something of a fantasy trope to have a specialisation for characters, it's a genre staple for a reason: it works. In GOT in particular it could be put to fantastic use, especially if it is combined with a multiple character POV system in the same vein as GTA V. Do you elect to play as a Night's Watch Ranger, with stealth and arrows as your weapon of choice? Or a master swordsman hailing from Braavos? Perhaps an assassin trained at the House of Black and White? Or a lancer from the Mountains of Dorne? How about a skinchanger like Bran or Orell, warping into the skin of wolves or eagles? Or even a Red Priest of R'hollor? There are almost endless possibilities here, and if managed correctly would demonstrate vastly different play-styles. Synthesizing elements of a Final Fantasy style class system with a Skyrim-like upgrade and skill structure would make for a truly awesome gameplay experience. There's no denying this would be a huge undertaking, particularly if you had multiple characters and class systems, but the rewards would be oh so worth it.