That question will get a very different answer depending on who you ask. It is based on the tenets of Islamic fundamentalism, which denies equal rights to many people, and clear human rights abuses have been documented. When it was founded it had the stated aim of establishing a Muslim state, not only in its own territory of Gaza, but even in Israel itself, and has been responsible for many attacks on Israel. Hamas is not officially recognised by the US, Israel or the EU.
However, Hamas was clearly elected in Palestine in 2006, and has stated in recent years that it is willing to coexist with Israel if Israel returns the territories that it occupied after 1967. In 2009 Israel did withdraw from the Gaza strip but retained a lot of control over its borders, airspace and the movement of people in and out, so from the point of view of the Gazans it hasn't actually withdrawn. This is one reason for continuing support for Hamas; the party has also done a lot of social and medical work among the poorer Palestinians.