A dictatorship is an absolute overbearing power, usually in governmental form, where the people in the country have no freedom. But that is not the case with God. Heaven and hell are the only options available according to biblical theology. You see, heaven is the presence of God, and hell is the absence of God. You are either with God or not with God. There aren't any other options. So, God declaring that these are the options doesn't mean he's a dictator. It means he's informing us of how things really are--that there are only two options available.
Furthermore, people have the freedom to reject God and his great love shown to us in the person of Jesus Christ who was crucified, died, was buried, and rose from the dead for our sins (1 Cor. 15:1-4). If God were a dictator, then he would not allow people to make the choices to either follow him or reject him. If God were a dictator, he would force everyone to believe what he wants them to believe. Since God does not do this, he is not a dictator.