Question
Why should I obey the Jewish commandments if I don't want to? Shouldn't personal choice play a part in my religious observance?

Answer
"If I don't want to" is highly subjective. Try a different context. Can I say, "Why should I obey the traffic laws if I don't want to?" Regardless of your feelings, we can presume you do not drive on the wrong side of the road because you know you will endanger yourself and others, the law will punish you, and your conscience will feel bad about it.

Your possibly rebellious feelings are not necessarily the only criterion. Rabbi Aharon Lichtenstein, a leading Israeli rosh yeshivah, says:

"Conventional morality holds that anyone and everyone is entitled to do as he pleases provided that he steps on no one else's toenails; that, as master of his self, he is free to mould his own destiny. Halachah is radically opposed to this attitude; it holds that even with respect to his own personality, man is more trustee than master.... The whole of halachah is grounded in profound faith in man's capacity to choose freely and to chart his own course. It is precisely this faith which makes the stress upon duty - the incessant call to respond to commands - possible. Halachah grants man less but believes in him more."

The crucial element is that though the Divine command comes from above, man freely and voluntarily responds to it.