I very much liked the passion. Gibson's take on the events was very focused (In catholic circles the phrase "the passion of the Christ", if I'm not much mistaken, refers to exacly what Gibson portrayed in the movie, the immediate events leading up to the resurrection)
As a Mormon I believe that the bulk of the suffering occurred in the garden of gethsemane. The physical aspect of Christ's suffering at the hands of humans took on a great deal of poignancy in the film because it was so totally in line with what might have happened, and so unnecessary. (Pilate sends a man down to the punishment squad with instructions that he be "severely" punished and you get what Gibson portrayed, including the head sergeant putting a stop to it a little late(he had other things on his mind)) Christ was enduring what he had to in order to fulfill prophecy and die at the hands of the Jews. The physical torture was merely the road he had to travel to get to that end. And no matter how unnecessarily bad it got he couldn't quit if he wanted to fulfill his father's will. And, for me at least, the suffering that happened in the garden is totally inaccessible. I have no basis for comparison and therefore no understanding of what it is like to spiritually suffer for the sins of others. The physical torture, while seperate, is the only part of Christ's trials I have any hope of understanding. Watching his treatment spiral down in such a totally realistic way made the knowledge that it was merely the icing on the cake much deeper and more real for me.
On top of that was the absolutely impeccable and realistic performances of the supporting cast. In most LDS films Christ and everyone who has anything to do with him is portrayed as ultra-serious, ultra-pious, totally-in-control-at-all-times, and thus stiff and unrealistic.
And the feeling I got from Caviezel's performance that even Christ was operating on faith all the way to the very end was especially precious to me.