Is Sunni versus Shia the main division in Islam?

**Is Sunni versus Shia the main division within Islam?** I've heard this many times, but I don't trust everything I hear. Also, are there any groups in Islam which see itself as separate from both Sunnis and Shias, and sees those two groups as belonging to a larger group? For a Christian analogy, I've heard that the Russian Orthodox Church split off from the Roman Catholic Church before the Roman Catholic Church split into Roman Catholicism and Protestantism. The Russian Orthodox Church would see Roman Catholicism and Protestantism as belonging to the same group.