I know my sheep and my sheep know me. - John 10:14
When Jesus describes his relationship to us, he repeatedly uses the picture of a shepherd taking care of the sheep. The shepherd knows who is lost, who is hurt, who is tired. He knows where they live and whether they have enough to eat. "He calls his own sheep by name and leads them out ... His sheep will follow him because they know his voice" (from John 10:3-4). There is a bond of love and trust that is the most important part of making sure nobody gets lost.
The biggest problem with the megachurch is not all the things which can go wrong with the theology or the leadership. The biggest problem is what is sure to go wrong because the leader does not know each of his followers well enough to do his job of shepherding. Teaching and inspiring are only parts of the job of a pastor. If the pastor does not know who is hurt, who is tired, who is lost, if he does not know his peoples' names and where they are staying, if he does not know who is hungry, then he is not doing his job. "He makes me lie down in green pastures" (from Psalm 23); the shepherd knows who is tired in this overworked, overbusy culture and insists that they get some rest.
The problems can be traced back long before the megachurch movement. Pastors may perceive their job as teaching their people or inspiring their people. While that's part of the job, some have forgotten that this is not their entire job. American mass culture is very efficient -- but people get lost in the shuffle. We have let church become a place where people can get lost in the shuffle, even though our communities should be the last place on earth, the light on the hill, that people can call home. This is more important than ever in this era where fewer and fewer people have families on which they can rely.
I do not mean to suggest that the problem is limited to megachurches; only that, in megachurches where people come and go unnoticed unless they fill out a form, the problem is inevitable.
Update: To make the long story short, I think the missing ingredient is fellowship, which is the human aspect of it all. There's no fellowship between the pastor and the congregation, and most members have no fellowship at all with most of the other members.