Secondly, I actually don't believe there is all that much in the film specifically "Catholic" at all. What is there is explicitly biblical, for the most part. We can all agree on this. It has been said a lot that Protestants don't emphasize the suffering of Christ as much as we do, and tend to go right to the Resurrection and Glorified Jesus (I heard a Protestant scholar from Fuller Seminary on a news show yesterday humbly concede this very point).
This is true, but I would contend that it is not intrinsic to Protestantism. I think it is a failure in practice and in emphasis that has come about probably largely due to over-reaction against Catholicism.
It's not inherent in Protestantism because Lutherans (the original Protestants) have a robust theology of the cross, and traditional or "Anglo-Catholic" high church Anglicans hold to many of the same beliefs and emphases that we do. Many individual Protestants of many stripes do not fall into this trap. I was never of this mindset when I was a low church evangelical Baptist-type Protestant -- who didn't care much for liturgy or sacramentalism -- (though I certainly understand these things better as a Catholic than I used to). We would put out our little sculpture of Michelangelo's Pieta during Easter season just as we do now. We understood this. It was common (biblical) sense.
I have a little semi-humorous response that I make when a Protestant asks me why I am concentrating on Jesus on the cross when He is in heaven now. I ask them, "then why do you reflect upon Jesus in a manger as a baby at Christmas, then?"
Failure in practice in Protestantism is the same as the failures in practice of Catholics; e.g., our abysmal lack of Bible knowledge and Bible study. That is not intrinsic to Catholicism, but it is, sadly, the way things are for many, many Catholics (for a variety of reasons), and Protestants understand this far better than we do. We can help each other and complement each other. Likewise, the ignorance of Church history among many Protestants . . .
That said, I do think there were arguably some particularly "Catholic" elements in the film (in some sense) and I will now note them. One was the wiping up of the blood of Jesus after the scourging. That is very "Catholic" because it constitutes a relic. But even here, this is a "biblical thing" at bottom, not a "Catholic thing," because the Bible reports how the bones of Elisha brought a dead man to life; the shadow of Peter healed people, and Paul's handkerchief did the same.
Therefore, to the extent that Protestants would frown upon this, they are not being as "biblical" as we are. Ironic, isn't it? Opposition to this would be every bit as irrational and unbiblical as opposition to crucifixes or meditation upon Jesus' sufferings in the Rosary or in other ways. It so happens that we Catholics "get" this and many Protestants don't, but that doesn't make it intrinsically "Catholic" -- just "Catholic-practiced" and (mostly) "Protestant-ignored."
One might say that the big role for the Blessed Virgin Mary in the film was a "Catholic thing." I don't see how, because this is simply historical fact. We know from the Bible that she and John and a few other women were the only followers of Jesus present at the crucifixion. So it is not unreasonable to assume that she was present for some or all of the other proceedings (especially since it was all on one day and mostly in one area). Mainly it shows her following Jesus and suffering with Him, empathetically and maternally.
This is simply history (or reasonable assumptions about what probably occurred). It is no more "Catholic" (whatever one's Mariology might be) to show a mother concerned about her son being tortured and killed than it is to show John watching the whole thing, too, or for any of us "watching" vicariously through the medium of cinema.
The film presents a visual representation of the "Pieta": Mary holding her dead Son Jesus (as in Jesus of Nazareth which had a very moving similar scene -- that gets me every time -- , but with Mary wailing uncontrollably). Is this peculiarly "Catholic"? If it is, it is only insofar as Protestants wish to deny that it might have happened just like that, since Mary was at the cross, and loved her Son, and would want to hold Him even in death, as the natural impulse of any mother (or father) would dictate. So I just don't see it. That is not Catholic theology (i.e., no more Catholic than Protestant): it is simply being a normal human being and a mother.
What I found very "Catholic" myself was the careful way in which Gibson portrayed Mary: she was (of course) extremely distraught and in agony, yet it was with a certain stoicisim and acceptance that this was the way it had to be (and this interpretation was followed through in the "pieta" scene as well).
She knew her Son came to die and redeem the human race and she knew it early on (arguably from Simeon's prophecy (Luke 2:35) but in all likelihood earlier, because she knew He was the Messiah (right from the angel at the Annunciation) and if she knew her Scripture she would have known that Messiah was to suffer and even die for us (e.g., Isaiah 53). Furthermore, He talked about it quite a bit. The disciples may have been dense about that, but it doesn't follow that she was, too. She heard this and understood it. Views about the "ignorance" of Mary with regard to Christ's mission are unbiblical, implausible, and "liberal" in the same way that views about Jesus' "ignorance" are.
Therefore, Mary willingly accepts His passion and death. That doesn't mean she was overjoyed about it (any more than Jesus Himself was); only that she suffered in a way that excluded the total despair of a person who has lost all hope and sees no meaning whatsoever in some suffering or calamity. There is a huge emotional and existential difference between despair and a distraught state and utter, black despair without hope or meaning.
I believe Gibson was consciously aware of this and incorporated it into the film; otherwise Mary would have cried and carried on much more than she did (just as we viewers cried and carried on).
Lastly, here is what I thought was perhaps the most distinctively "Catholic" moment in the film (and no one I have yet read caught it). It's just my opinion and mere speculation, but see what you think: During the "pieta" scene, Mary looks straight at the camera for a long time and I agree that this could be read as her saying "why did you do this to my Son?," or "look what love my Son had for you."
But a detail I noticed was that her right hand was opened, either heavenward or towards the viewer (I'd have to see it again). That might be construed as Mary offering Jesus her Son up to the Father, much in the way that we participate in the Sacrifice of the Mass every Sunday. This is quite Catholic. My wife noted that it might also signify Mary saying, "come accept the salvation that my Son just made possible by His horrible suffering." Mary in turn helped make that possible by bearing Jesus in the first place (being the Theotokos); thus participating in the Incarnation, without which there is no Redemption.
Does that make Mary equal to God or Jesus, or make her role in salvation history at all equal or on the same level as the work of Jesus. No, no, and NO (with the highest emphasis). But it does make her a key human "player" in redemptive history. And that is very "Catholic" indeed, but also -- I firmly believe -- not contrary to biblical teaching, even if not explicitly spelled out in it.
But I admit that this is speculation based on one observation of a gesture in the movie. Take it for what it's worth. If Gibson ever confirms this, then my impression will have been justified.