Like all the others here I also find delayed withdrawal and poor support as the two main reasons why will you feel annoyed and drive you crazy, you have won a big amount and you cannot withdraw and the support is ignoring your messages you are left in limbo, you have left no reason but to post in the scam section worse thing is the casino you've played with has no support or representative in Bitcointalk.
Having poor support is one of the worse. When you're in need of help and there's no one to respond you from what you're experiencing on their own casino, it looks like you're being ignored and not being taken care of even though you're a genuine customer.
Good thing on me, I haven't experienced such bad support or lack of response to the concerns that I've sent to the casinos that I've played. They've always been responsive and helpful and the most important, friendly.
When they're friendly with how they talk to their customers while having those issues, the issues are being forgotten and the customer will remember how good the support is and that's making them comfortable and will make them back to gamble again.