Is that a direct port or is there stuff added or taken away? It's 5 flocking CDs so it's huge! Well, Substance adds graphical tweaks, a chance to play as the Cyborg Ninja and other characters, new costumes, VR Missions for Raiden, mini-games (such as skateboarding) and... If it's anything like the PS2 version (although I have just the original), it galleries like character models, how the AI works etc. etc. If someone owns the original MGS2 already (the PS2 version), then Substance isn't really needed, despite it's extras and other stuff.