I've heard stories about churches buying tickets for this en masse in the belief that it will convert people, but having seen it I really can't see why. As a committed non-believer (nay, heathen), it just came across to me as a story about stupid people getting whipped up into stupid actions by religious extremism, with stupid and contemptible results. Not understandably misguided and tragic: just stupid. And I'm afraid I include Jesus in the category of 'stupid people' there.
The Passion is definitely capable of being put across in a more compelling way than this. Bach's Passions (the St. John and the St. Matthew), and the relevant parts of Handel's 'Messiah' (which I'm listening to right now because a biblical quotation at the start of the film brought it instantly to mind) make this very clear. OK, so they could never convert me either - but at least they have an emotional impact on me. Bach and Handel make the story seem like an regrettable human tragedy, but somehow Gibson's failed to engage me emotionally in any way.
I think the problem could be phrased as being that the film was 'plot-driven' rather than 'character-driven': in other words, we just got a sequence of canonical events from the gospels, rather than any recognisably human scenes which might help us to relate to the characters or make sense of the transitions from one event to another. There was one scene which almost managed this, which was when Jesus fell down while carrying his cross to Golgotha, and Mary ran towards him to comfort him, which was interspersed with a flash-back of her running to pick him up when he fell and grazed his knees as a child. That gave us a chance to feel human pity for the motif of a mother losing a son she had raised. But other than that it left me cold (except for the occasional 'yuck' at the abundant violence).
I asked James, who is training to be a priest, whether it engaged him on an emotional level. He basically said that it had stirred the same sorts of emotions in him as a regular meditation on the stations of the cross would have done, but that these were emotions which he'd brought with him into the film from his church experience, rather than emotions which the film had stirred in itself. Yet obviously it has stirred great emotional responses in some viewers, because there are stories in the recent edition of The Cherwell about people confessing to long-undetected crimes after having seen it. I wish I could understand how it managed to do this: possibly those people also had to bring pre-existing emotions into the film, which were then sparked off onto a new level by it?
I wasn't too happy with the Latin either. I'd need to see it all written down to decide what I thought of it properly, but many of the sentence structures sounded very English, I spotted at least one example of someone not using the vocative when they should have done, the soldiers who are scourging Jesus inexpicably start counting from eight after they have turned him over to start whipping his front, and all the Romans used pronunciation which was a cross between medieval Latin and modern Italian. Plus, why were the Romans speaking to people like the Jewish high priest in Hebrew? At least, I presume it was Hebrew, although I can't distinguish Hebrew from Aramaic: but it certainly wasn't Latin or the actually-more-likely Greek. That doesn't fit with my knowledge of Roman provincial administration, although I'll admit that Judaea wasn't entirely a typical province, and I don't know much about its specifics.
And on top of all that, they also rather gave the game away for the sequel by showing him sitting up in his tomb at the end! So much for Passion II: The Resurrection.
Ah well, at least I've seen it now... I expect to enjoy 'Troy' a lot more when it comes out next month.
 Isiah 53.5: 'He was wounded for our transgressions, He was bruised for our iniquities; The chastisement
for our peace was upon Him, And by His stripes we are healed'.
 And no, they're not carrying on from where they'd got to on the previous side, because they'd reached about twenty-something on his back.