I haven't been through "D" in ATL since last December (I think). To me it was sufficiently maintained. Sure, it isn't as polished as "F" or the recently renovated "B" in ATL. It is narrower than the other concourses and used to be regional, but now it is a combo of regional/mainline. Personally I think ATL is one of the best maintained airports in the US. With the worst being SEA.