Metal Gear Solid 2: Substance is a multi-platform updated version of the original MGS2 released for the PlayStation 2, as well as the Xbox and PC. The game contains the main Sons of Liberty game with some subtle alterations (including a new infrared effects for the thermal goggles and a new set of dog tags), as well as the inclusion of Boss Survival and Casting Theater modes (neither of which were included in the original North American release).

The main addition of Substance is the inclusion of nearly 500 stand-alone missions (similar to those from Metal Gear Solid: VR Missions) with 300 missions set in a VR environment (including a set of missions played for a first person view) and 200 "Alternative Missions" (including bomb disposal missions) that take places in areas from the main game. In Missions mode, the player can choose between Solid Snake and Raiden, as well as unlock alternate outfits for both (such as Raiden in the Cyborg Ninja exoskeleton and Snake in his original sneaking suit from Metal Gear Solid).

Secrets

Enhance Grip Level Easier
You can enhance your grip level by doing 100 pull-ups on a ledge, or you can do 10 drop-and-catches. To do a drop-and-catch, find two ledges which are parallel to each other. Hang off the higher ledge, and press X, then repeatedly press Triangle. You should grab on the lower ledge. If you do this 10 times, you get an enhanced grip level. There are 3 total grip levels. Two ideal places to do this are the Tanker's Engine Room, and the Plant's Strut D.

Guy on toilet from MGS1
When you get to the Shell 1 Core and you're supposed to listen in on a conversation between Solidus and Ocelot, point the Directional Microphone over to the left near the stage and you should hear Johnny from MGS1 talk to himself. It has a hilarious ending.

More grip
If you hang on a ledge and press L2 and R2 you will do a pull-up. If you do enough of these, your grip level will rise. The maximum is level 3.

Unlock all Characters for VR Missions
If you are lucky enough to have The Document of Metal Gear Solid 2, complete all 5 VR Missions. Have this memory card inserted when you select VR Missions on the Substance disk, and you will have all 5 hidden characters unlocked from the get-go. You will have 00% for each character despite finishing the 5 VR Missions on TDoMGS2.

Here's the intro of a pretty good MGS title: