The Rambam, of course, is justifiably famous for his 13 Principles, which are today understood to be the foundation stones of Orthodox Judaism. What we sometimes forget, is that Jews didn't immediately accept everything the Rambam said on the day that he said it.
People disagreed (strongly) about various points for years --even centuries-- afterwards. Even today some observant Jews demonstrate through their behavior and beliefs that the Ikarim aren't fully accepted.
In this fun post from 2005 I go through the Ikarim and show how some of them are still disregarded in both modern and Hasidic communities: Orthoprax Koferim: Teaneck vs.Williamsburg