Well, there are 2 endings to Fatal Frame III, the second one is only available to obtain once you've gone through the game once already.
*SPOILER WARNING*
So, 1st ending, full cinematic FMV, pretty decent, Rei see's Yuu again. I like it that in the US version Yuu completely takes on Rei's tattoos. (JP version he takes them away, but they don't transfer to his body). It's emotional and sad and great.
The only bad thing about the ending is that it leaves Mio's fate ambigious...and a lot of fatal frame fans still argue if she survived or succumbed to the curse etc. Since she's loved as much (if not more) than Miku, the first ending kinda hurts her character.
I also really would have loved an optional ending where Rei fell pray to the curse. :> Her surviving, when everyone else around her seemed to have a much stronger willpower and desire to live, seemed completely unfair.
Ending 2 - I *REALLY* like this ending because Kei survived. His 'hiding' ability aside, Kei is a really interesting character....and I dislike it that when you play the game the first time he 'dies'. The only nitpick about the second ending, is that Project Zero pulled a 'Fatal Frame Xbox ending' with this ending. The FMV is exactly the same (save for being cut off right before Rei starts to cry)...and the credits run...with photographs of 'what happened afterwards'. It really would have been nice to have a fully rendered FMV. I would have waited several months more for that if needed! :>
It is a 'nice' ending, because the Photos show Kei introducing Mio to Rei & Miku, thus showing she survived and was OK.
So yeah, I don't know...if you're asking 'is it worth it', I definately think it is for a first runthrough...if you're like me and want all the costumes and accessories, then definately play through a couple more times.

But, after FF2 with its larger variety of endings, FF3 seemed to cut extremely short in that department. (Even when FF1 did do a photographic ending for the Xbox version of the game, the game already did have two fully rendered completely different endings)