Defining Roman Catholicism

Had a really interesting conversation with a staunch Roman Catholic the other day. Interesting because (as I told him), I'm certain he would have been branded a Protestant and joined the Reformation if he was alive with Martin Luther and John Calvin. And I'm convinced he's saved.

He does hold to many 'official' Catholic doctrines which (I think) we all disagree with, but he holds them in a way which is ALMOST Biblical in my opinion (although I still disagree) :) Even more strange - he is certain that his beliefs are official Vatican-endorsed doctrine. Yet they differ drastically from what I think about Catholicism, based on my experiences with other Catholics, my readings from Roman Catholic authorities, and of course many Protestant teachers.

I'm not going to detail his beliefs here, as he may read this post. And I don't want to mis-represent his views! But I just found it extremely thought-provoking. And I wondered if it would be helpful to discuss it here:

1) What differences are there between Roman Catholicism and Reformed Protestantism?

2) Do these differences actually exist - for the Vatican, for all Catholics, for just some Catholics? Do they (or similar differences) exist between groups of Reformed Protestants?

3) Are these differences actually important? Why? Are they more important than differences that exist between groups of Reformed Protestants? Why?

4) Are there ways to hold to these points in Catholic doctrine, which minimize the difference or minimize its importance?

Please comment away!