I never really cared for "Man with the Machine Gun" until I heard this version way back when I bought the FF S-Generation CD. (I actually preferred the normal FFVIII battle music)
Then there's the legendary One-Winged Angel which was much better as a metal song. (SPOILER)
I also like how they overlaid the metal onto the orchestrated version.Also the new lyrics was a nice touch.
Any other songs you can think of that were substantially improved by being remade?