From Tim Challies:

Osteen cunningly blends the wisdom of this age with language that sounds biblical. He blends the most popular aspects of New Age and self-help teaching with Christianity. And his audience is eagerly drinking this in. And this raises an important and related question. What is Osteen’s authority? On what authority does he base what he teaches?

Christians have long understood that the only authority we have when it comes to spiritual matters is authority given to us by God through the Bible. We are committed to teaching only things that are consistent with God’s revelation of Himself in the Bible. Without the Bible we have no authority. A pastor has no right to stand in front of a congregation and teach people what he believes. Rather, the pastor is to stand in front of the congregation and teaches people what God says about Himself. He bases all he does and says on this standard.

In reading Joel Osteen we do not see this manner of authority. In reading Osteen we see a man who appeals to himself and to his own understanding and experience as authority. (Online source)