I think it was a quite good movie, but overall it's too... depressing. I understand the point of the conclusion, but it just leaves me with a bitter taste in my mouth. I would've much preferred the original ending that was eventually changed.
SPOILER INCOMINGIn the original script, Morgan Freeman's character is the one who kills John Doe, in order to save his partner's soul and sanity. It even was requested by the actors that the head of the girl is in the box, it was going to be a dog head as far as I know.