The main problem with Joel Osteen is that he preaches a very lovely suger-coated version of what following Christ meants. It is a combination “word of faith”/“prosperity gospel” philosophy. The basic belief seems to be that if you have faith, anything you want will be yours (based on an interpretation of Matt 11:22-23). Oh, and God wants you to have a nice house, send your kids to college, get that big screen TV.
Unfortunately, he leaves out where Jesus says you must take up your cross, where Jesus says you will be persecuted, that what God wants for you may not be what you want for you.
He also doesn’t seem to believe that we will be given new bodies (resurrection of the body), but has said that we will live on as spirits.
It’s hard to know what else he does or does not believe as he doesn’t talk about things like sin since those are too depressing.