"What do you think?" sounds quite casual and informal, whereas "According to you..." and "In your opinion..." are quite formal.

so there's no exist something make it really different?

These are all the same thing but can be used in different contexts. Like what do you think can be meant literally and have no connections to any topic. You just merely want to know what a person is thinking. However these three questions are commonly used in the same context and mean the same thing