IMHO, the first and third books in the series are some of the finest fantasy books ever written. The second book is right up there, but the forth (A Feast for Crows) was a bit disappointing. Why? It concentrated on new characters who I didn't care about as much and the plot moved too slowly. A Dance with Dragons suffers from some of the same problems as the fourth book. A few new characters are introduced, and portions of the plot move pretty slowly. However, it does develop the journeys of some of the characters that we've known from the beginning, which is really nice to see, and, eventually, some major plot developments occur.
A have one other criticism of Dance: its too dark. You'll rarely hear that from me when talking about fantasy. I'd rather have me some dark stuff than trope fairy tale unicorns and rainbows . But, at the end of Dance I felt beaten down. How depraved can a world and everyone in that world be? Is there any hope that Westeros will survive? Do I even want it too survive? Please, George, I'm begging you! Give me some ray of hope!
So, bottom line, it is worth the read, especially if you're already a fan of the series, but don't go in expecting to be blown away like you might have been with the earlier books. And lets hope we don't have to wait another five years for the next one!