Disagree with your "overall," comment. They may suck locally for some people but overall their network is extemely large and robust. They have had specific capacity challenges in some metro areas but they also have the higheset concentration of smartphones of any US wireless carrier.
I believe the iPhone exposed them to initital criticism and they never recovered the premium image. I would go as far as stating that many people who rag on AT&T online no longer use them but they still feel their 2008 opinions are still valid.