As much as I love both GRRM and Tolkien, I will say this. It is incredibly unfair to compare anyone in world building to J RR Tolkien. The man was a fellow at Oxford and a tutor at Pembroke college. He was fluent in Anglo Saxon and had a very good knowledge of French, Italian, Latin (obvs), old Norse and various Celtic languages. GRRM is a writer, Tolkien was a scholar (the man went to my old school, so knowledge of him was practically compulsory). People calling GRRM the 'American Tolkien' is unfair both on George and on Tolkien, they are different as night and day.
Tolkien based so much of his world building on knowledge of the Ango-Saxons (his first love) as well as his time in the trenches, GRRM bases a lot of his writings on his refusal to fight in Vietnam. Tolkien spent a lot of his time inventing languages as the linguist that he was, GRRM allowed others to invent his languages for him. Both created detailed lineages for their important characters and both showed the horrors of war, Yet to compare the two is both disingenuous as well as intellectually dishonest. AWOIAF can no more be called GRRM's Silmarillion than Twilight be called a modern Dracula.
This is not to say that I did not enjoy AWOIAF, but it was still wank in places. Grover, Elmo and Kermit are my main examples, but over stuff (by Elio and Linda mainly) was atrocious.
I suppose most of my dislike comes from people who DO compare the two, and say that Tolkien's writing was boring and his worldbuilding was awful.
Fuck, GRRM respects Tolkien's writing.