What were the differences between the Jews and the Samaritans?

Answer 1

You can get the idea of a main one by the things the Pharisees said about Jesus:

Then answered the Jews, and said unto him, Say we not well that thou art a Samaritan, and hast a devil? (John 8:48)

Answer 2

According to Jewish tradition, Jewish history begins with Abraham 3800 years ago, while the Samaritan religion started a millenium later. After the Assyrians exiled the Israelite Ten Tribes (about 2600 years ago), the Assyrian king brought non-Jews from Cutha, Babylonia and Syria (Hamat), and settled them in the depopulated area where the Ten Tribes had lived (Samaria). They were taught Judaism by one of the Jewish priests (2 Kings 17:27), and they were taught the Torah, which they wrote in the Old Hebrew script.

While both groups believed in One God, and both accepted the Torah (the Teachings given by God to Moses), there were also a number of differences. Jerusalem was and is the holiest site for Jews, while the Samaritans have Mount Gerizim as their religious center. Later in history, the Samaritans aligned with the Greeks and accepted foreign gods (Talmud, Hullin 6a).

The Talmud relates how the Samaritans adopted some of the mitzvot (Torah-commands) but not others (Talmud, Berakhot 47b), how they denounced the Jews to Alexander in an unsuccessful attempt to get him to destroy the newly-built Second Temple (Talmud, Yoma 69a), and how they interfered with the declaring of Rosh Hodesh (the New Moon) (Talmud, Rosh Hashanah 22b). Our traditions relate how the Samaritans would waylay the Jews who tried to journey to the Holy Temple.

Today the Samaritans are a small group of about 800, who practice an ancient form of Jewish worship, with animal sacrifices. They don't accept the Talmud nor holidays such as Hanukkah.