You know, that was one of the hallmarks of BtVS - none of the parents were good parents. They were poor parents in different ways, and Joyce was by no means the worst of the bunch, but they were all children of fairly dysfunctional families. That was one of the things that endeared the show to me - high school kids, left to their own devices, trying to survive and perhaps even thrive, on an open hellmouth.
No, Joyce was not a great mother actually. But she was probably the best of the mothers out of all the kids, so I guess that's why she was looked upon more favorably than I personally think she should have been.
And in fanfiction, I love me some Mean Joyce.
