Very nice, at first I thought it was decent, nothing more. Then I started scanning the forums and left it on loop. I swear I never knew the song ever started or ended. It was great, just leave this thing going and it grows on you. I could easily leave this on at night and sleep in an extra hour. I'm just afraid it will lose its luster after playing it so long! Lets hope not. It went from a 6 when I first heard it to a 10. I love this song, kudos.
A side note, (You will have to excuse me, I might be wrong on some of this, havent played the game in about 2ish years.) I thought it would be the main theme, as I enjoy that song over all of the other MGS tunes. But to my suprise it was the very (IMHO) "ok..." end theme. I personally disliked the end song (not the one with the choir). But if this is the end song then you sure did change my opinion I simply love it now. (Once again, I might have the tunes mixed up, hell, I'm not sure the main theme is even the REAL main theme haha! Please, enlighten me.)