METAL GEAR SOLID 2: SUBSTANCE is the first Metal Gear game with direct involvement from series creator Hideo Kojima that just doesn't have that immense attention to detail that have given rise to his success and praise.
After completing METAL GEAR SOLID 2: SONS OF LIBERTY in 2001, Kojima has gone on to Produce THE DOCUMENT OF METAL GEAR SOLID 2 (an interactive documentary), ZONE OF THE ENDERS: THE 2nd RUNNER, and Substance. All of these titles have shown flaws, and just don't quench your thirst as much as one would hope (ZOE2 being the exception, but Kojima had minimal influence in this game).
Currently, Kojima is working on a true sequel to MGS2, a light-sensitive GameBoy Advance title (BOKTAI), and possibly an online Metal Gear title, so Substance most likely didn't receive the attention it needed to promote sales from anyone not idling HK's work.
The Sons of Liberty game (included in Substance) remains basically the same, with some very minimal changes (such as about a minute of added cutscenes originally cut and slight icon or display changes). The Boss Battle and Casting Theater modes make their first appearance on American shores, after Japan and Europe got them back in late 2001 / early 2002, respectively.
The Missions included are on par with those in the previous METAL GEAR SOLID: VR MISSIONS title after the release of METAL GEAR SOLID, and offer hours of additional gameplay. While fun, you just don't feel like you're _doing_ anything.
The Snake Tales are interesting alternative "episodes" starring Solid Snake, yet again lack Kojima's usual polish by relying on screens of text to convey the story versus full cinematics.
Finally, the Skateboarding feature is a fun addition (not included in the Xbox version released late last year), but Tony Hawk faces no competition from Konami's EVOLUTION SKATEBOARDING, whose engine this feature uses.
In the end, '1337' Kojima fans will pick this up and enjoy the new missions (if they haven't already purchased the Xbox counterpart), but for the rest of us, there's no reason to buy Substance unless you haven't played MGS2 before, and if you haven't, you probably shouldn't.
