The main thing I want to say about this game is that in some ways it is as good as a good novel. It is so immersive, so atmospheric, and so beautiful.
(In some ways it can be likened to Another World on the Amiga, which also made you care about your computer companion, and had the best, most intelligent and artistic cinematics of its day, far better than those in its sequel Flashback.)
I love the ending, but I agree it arrives too soon, and that replay value is not high. But in terms of story-telling it is easily the best (in my) experience on the ps2, and puts Metal Gear Solid 2 to shame.