Aww, you think he will finish the saga someday.
Anyway, the beginning of A Song of Fire and Ice is indeed incredible. It started going downhill gradually, A Feast for Crows was already a slog, until I gave up reading it in the middle of A Dance With Dragons. So many plot threads not heading anywhere.
George Martin uses a "technique" that he calls "gardener writing style", in which the author doesn't really plan the story, they start it with some ideas, and create stuff as things go. And it really shows in A Song of Fire and Ice. That's why it starts awesome, but it loses its way quickly and characters don't really seem to know what they're doing or where they're going.
I think this writing style works well in smaller books, but in a saga with soooo many characters and plot lines, it's impossible to keep it interesting or cohesive enough. I've read he wanted to make a book trilogy originally. And then since he doesn't have a clear plan or goal, it bloated and he started thinking about 7 books. And now people are discussing even with 7 books, it will be really hard for him to finish the whole story and all plot lines. And judging by the time he's taking between books 5 and 6, it's silly to think he'll ever really finish it.
Also, he's already 73 years old.