I have been a member since 1974. If you differ from the Pope in your beliefs ("We're right, everyone else is wrong, neener neener neener"), it might be a good fit for you. Most Christians think theirs is the One True Path. There are Mormons, Presbyterians, Baptists and Methodists who echo what the Pope said, in their own way. (That was the Roman Catholic Pope, Benedict, not the Greek Orthodox one, the Assyrian Orthodox one, the Armenian Orothodox one . . .)
If you leave this question up long enough (sometimes 20 minutes is enough), someone will say we are a cult, and someone else will say we are "The church that doesn’t believe in anything."
Cults have three hallmarks, according to the dictionary. 1) They are relatively new, 2) they have a single, charismatic leader, and 3) they share a single mindset.
1) We have been around for 200 years. President John Adams and his son, President John Quincy Adams, were Unitarians.
2) Our leader, the president of the UUA, changes every five years. Sometimes we elect a person with charisma, sometimes we don't.
3) Some of us believe in God, some don't. That is the widest variety of "mindset" you'll find in any religion today.
We are not a normal denomination, but we are far from being a cult. Calling us a cult is like calling Donald Trump a socialist, but that doesn't stop people.
On to beliefs: There are Presbyterians who vote Democratic and Presbyterians who vote Republican. No one calls them "The church that doesn't vote for anything". There are Lutherans who eat lima beans and Lutherans who do not. No one calls them "The church that doesn't eat anything". There are UUs who believe that God exists, UUs who believe that God does not exist, and UUs who believe that the nature of God is beyond human comprehension. This upsets people and they call us "The church that doesn't believe in anything."
If you join a Christian church, you believe in the Father, Son and Holy Spirit, that Jesus was born of a virgin, that Mary was born without Sin, that everyone else was born covered with Original Sin the way seagulls get covered with goo when an oil tanker springs a leak, and so on. UUs don't all believe the same thing about the nature of God. All of us have thought long and hard about it, and we all have our own beliefs about it.
Our common beleifs have to do with actions. We all believe:
1) We value "The worth and dignity of every person". We take "worth and dignity" seriously. That means even if he is black, white, brown or red; even if she is poor or a lesbian; even if he is gay or homeless, or she used to be a man, or he stammers because he has an IQ of 140 trapped in an 80-year old body that suffered some strokes, or her legs don't work. The gay or lesbian part usually upsets conservative people.
2) A free and responsible search for truth and meaning. In practice that means we question some parts of the Bible and that most of us believe in evolution.
3) The democratic process. In practice that means each congregation hires (and fires, if they deserve it) their own minister, instead of having a bishop send us a new one. We have more librarians and ACLU members per capita than some other churches.
We have four other principles. Those three are the ones you hear about most often, and the three that set us apart from some other denominations.
If you'd like still more, I maintain the web site for my congregation:
http://www.stanuu.org/beliefs.html
http://www.stanuu.org/newfaq.html
Our national organization has a much more comprehensive web site:
http://www.uua.org
Ours has better jokes.
If you'd like LOTS more, our site has 40+ sermons, a dozen from our minister, two dozen from guests who are lay people. I wrote three of the sermons on the Guest Sermons page, including one, "The Devout Unitarian Universalist", that was inspired by questions on Yahoo! Answers.