If we were to look at this from a non-believers perspective, there is normally one question that stands out, "Why would a kind and loving God send me to hell?" While we can't answer that with a direct answer, we can answer it with a counter question, "Why would you deny yourself a place in heaven and everlasting life just to live of the world?" These are often the questions I have heard when trying to rationalize Christianity.
A religion claiming to be full filling another religion has to prove itself. But With Judaism the religion itself cannot be full filled, only the prophecies, which Christianity failed. Christianity is not rational because it claims to know Judaism better then Judaism. It changes almost everything, and worships a different god. All of which is forbidden in Judaism.
If you were to read the so called "Old Testament" aka the Jewish bible, without a persuasion by Jew or Christian, You would come up to a completely different conclusion of the religion, that doesn't even allow for Christianity to be considered legitimate.