I think I know what you mean by self-expression. In the West, being Buddhist is often presented as a way to further a person's goals, through finding relaxation or calmness. Since Buddhism is free from living for an all-encompassing God, it certainly has the sense of freedom to it; not sure if this is actually true though. The requirements for being a Buddhist will vary widely depending on which branch of Buddhism you choose. In this sense, the freedom to choose which Buddhism you follow is certainly wider and offers more room for choice. Yet, I don't think that the serious Buddhist life is open for a lot of self-expression. I would certainly not consider the 277 rules of a monk from the Vinaya as an example of personal freedoms. For example: not to show the tongue when eating, not to wipe the inside of your bowl, not to swing your arms when around other people or to laugh out loud when around other people. I don't think this fits with most people's idea of free self-expression.
Buddhism certainly offers a wider choice of options in what being a Buddhist means.