The sticking point between Catholicism/Orthodox versus Protestantism really comes down to one major issue, the rest being minor issues. (e.g. transubstantiation or intercession of saints are minor disagreements)
The big schism is sola scriptura (bible alone) versus bible+tradition. The Catholic/Orthodox believe that faith alone is not sufficient for salvation. They rather believe that works/sacraments must occur to maintain salvation. Skipping mass on a Sunday for example, puts a Catholic's salvation in jeopardy until pennance occurs. In protestantism they believe the Bible's authority alone shows that salvation is certain and via faith-alone, no sacrements required to maintain or support salvation.
Protestants would point to the thief on the cross that Christ stated would be with him in heaven...yet he didn't get baptised, circumsized, go to mass, receive an indulgence, belong to a church, or other later added tradition/sacrement.
The Catholics and Orthodox would point to their church traditions as supporting their doctrines because they believe their Popes or Patriarchs can speak Ex Cathedra, creating policies on equal-plane with written scripture.
That's the schism in a nutshell, everything else is friendly inter-denominational minor disagreements that are not considered "major" by most Trinitarian Christian faiths.