Joel Osteen is good for making people feel encouraged... that's about all he talks about though. Never a word about God's justice. Heaven is okay to talk about but never death, hell or salvation. And like a lot of other tv preachers he teaches the "health wealth, prosperity gospel" which is extremely dangerous to Christianity. It assumes part of God's love is to give us everything we want. The Holy Bible teaches that we will have what we NEED not what we want (Philippians 4:19). Note that this passage is in the context of giving away one's money for the purpose of God's Kingdom. (If live a lifestyle of a person in a third world country you have a better perspective of what a need is as compared to a want.) He basically tells people they are meant to live a life full of worldly success, and wealth. The Devils message equates success with earthly wealth. So yeah. He's teaching what the Devil would. Jesus teaches in the Holy Bible teaches that we do not store up our treasures on earth, but in heaven where no one can steal it (Matthew 6:20). Also from Philippians 4, I bet you've never heard the context of that verse that says we have strength to do all things through Christ who strengthens us. He was talking about being wealthy OR POOR. "11 For I have learned in whatever state I am, to be content in it. 12 I know how to be humbled, and I know also how to abound. In everything and in all things I have learned the secret both to be filled and to be hungry, both to abound and to be in need. 13 I can do all things through Christ, who strengthens me. " Also, he doesn't say that Muslims will go to hell, rather he'll say it's up to God to judge. It's on youtube, not that hard to find.
The health wealth prosperity gospel puts an attitude of entitlement to a Christian, or anyone else who listens. If I don't get what I want then there must be something wrong with God, because He isn't doing His job. And many people lose faith because bad things happen to them when the Bible says in Hebrews 12:6 "For the LORD disciplines those he loves, and he punishes each one he accepts as his child."