The Roman Catholic Church at the time of the reformation was not a perfect organization, to say the least... and a number of the practices that were objected to by the original Protestant groups are no longer approved of by the Church. I think the vocubulary differences that you get into are less as in 'not Christian' and more into 'fallen into error'. Please don't take offence if you're Catholic, I'm trying to use historical wording there. The point of the original reformers was not that it was not 'Christian' in that it didn't profess to follow the teachings of Christ, but rather that have added to those teachings to the point that the saving message of Christ had been obscured.
Remember, at the time of Luther, Calvin, Zwingli, etc... the battles over theological differences were played out in the political and military sphere as well. Nothing like a few excommunications, death sentences, armies, and invasions to escalate a religious disagreement into cries of 'Papist!' and 'Heretic!'.
In more recent history, most of the Protestant denominations, and even some of the fundamentalist (very hard to define that term, btw...) ones, have begun to recognize more shared ground than differences with the Roman Catholic Church.
There are still some significant distinctions, and lingering distrust from a few centuries of political opposition. (Founding a Catholic church in the south of the US is still probably easier than founding a Baptist one in Rome.) But I'd say the cry of 'not even Christian' directed from Protestants to Catholics is largely a thing of the past.