The other books are still good. Other people will argue that they're not, but those people are wrong. The problem a lot of people have is that ASoIaF isn't like a lot of other series; it is essentially the story of two conflicts, and the first one is wrapped up with ASoS. The books after it show what leads up to the development of the second conflict, much as AGoT showed what led up to the War of the Five Kings; thus, AFfC and ADwD introduce a ton of new characters and settings that were not even hinted at in the previous books. Most people aren't used to series progressing like that, so they think the books are bad. They aren't; they just don't maintain the pace of ASoS. But then, it would have been very difficult to sustain that pace after the events at the end of that book. After you read it, you'll understand why.