How about a Jewish answer?
Protestant Christians believe in salvation from Hell by the acceptance of JC as one's personal savior and redeemer from sin.
Every single noun in that above sentence is not part of the belief system of Judaism.
We don't believe in Hell, therefore we don't believe there is anything we need "salvation" from.
We don't believe anyone needs a "savior" and we define sin as "missing the mark", not in absolute erms. So we recognize that each of us is a work-in-progress, striving to do better to approach G-dliness in our daily conduct.
We also believe that all righteous people will have a place in the World to Come, and that nobody will be damned because they worshiped G-d by the wrong name. That's a big difference between Judaism and Protestants; Protestants believe you'll be damned to eternal suffering if you don't worship precisely as they do.
Protestants believe that they have supplanted Judaism as G-d's Chosen People. This is called "replacement theology". They utterly fail to understand what it means for the Jews to be the Chosen People-- we were chosen to be a light unto the nations, to bring the word of G-d to the world, to be G-d's people and to keep the 613 commandments given us at Sinai. Sometimes we have done better at this than at other times, but the fact that we still exist as a people means that our Covenant still hods. G-d doesn't break promises!
JC and kashrut are trivial compared to these fundamental differences in world-view.
Or since I know the basic Jewish stuff more about Protestantism (nothing complex) would be great 