I got my grubby hands on the game today so here are impressions for you.
I'm not going to comment on the main game, since you can go look up a review of the PS2 version. Instead, I'll concentrate on the differences.
Presentation:
Still the same slicker'n'snot presentation. The extra features come by way of more options on the main menu. The presentation for the added content is much more bare bones than the main game. For instance, on the Snake tales, each mission starts off with a few pages of text that tell you where you are and you're going. There also isn't much in the way of cinematics or radio chatter here either.
Graphics:
Looks pretty much identical to the PS2 version. I didn't compare the games side-by-side (though I could if you demand it), but the Xbox version has slightly more defined textures from what I can tell. Also there seems to be a little more detail in Snake's face during the cutscenes. One thing that was incredibly disappointing: there was some major slowdown due to the rain effect on the tanker level. I'm guessing this has more to do with lazy porting than anything, but I suppose that it could have something to do with the fillrate. The quetion is if they weren't going to bother optimizing the rain, why didn't they simply take about half the rain out? Its not like it would have impacted the game that much! Other than that one instance, I've yet to run in to any slowdown. Looks a bit dated for an Xbox game, but still has excellent animation. Most of the additional content takes place in VR missions, which are admittedly sparse. But even so, there are nice touches such as the way bad guys "de-rez", the way bullet marks are labeled, and the "measurement lines" that extend from boxes and such.
Sound:
I haven't had a chance to hook it up to my 5.1 system yet (later tonight...), but I'm betting that it sounds much better in DD5.1 than in stereo on the PS2. I'm looking forward to hearing the score in 5.1 I'll have more details on sound later.
Gameplay:
Still the same great gameplay as SOL, except with a whole avalanche more of it. There are some refinements to the gameplay outside the normal missions as well. For instance, in the 1st person VR missions, they give you a wide variety of controller options. It's a good thing too, the default control scheme for the 1st person missions blows chunks. I mean REALLY. You can't even look around while holding out your gun without taking your left hand off the left thumbstick and moving it over to the right thumbstick. I recommend moving to the type 3 controls immediately for a much more Halo like experience. The question is, why don't they give you this option during the main game?!? It would have been awesome to be able to run around the main game in 1st person mode. Also, after having played Splinter Cell, it was frustrating to not have complete control over the camera. but if you liked the core gameplay of the previous Metal Gear games (and who didn't?) you won't be disappointed.
Lasting Appeal:
OMG! The main missions from SOL are a drop in the bucket compared to everything that is here. I've only grazed the surface. After completing a few 1st person missions, I checked on my status: 0.3%. 0.3%!!!! Not even one 300dth of the way through! And I think that was for Snake only! There are numerous other characters to play! Can all this possibly fit on one DVD?!? The only thing they could possibly add to increase the lasting appeal would be multiplayer. But this isn't really a MP game, and the stuff that's here should keep you busy until MGS3.
For those of you that have MGS2:SOL -
If you enjoy the core gameplay of the MGS and won't miss all the cutscenes and story development (I know I won't!), the aditional content alone should be worth the price of entry. If you were willing to forego all the story and details in favor of gameplay as you may have for the VR missions on PS1, you'll definitely enjoy Substance. If the story and varied locations are your thing and you already own MGS:SOL, then you may not get much out of Substance, and you'd probably be better off getting Splinter Cell instead.
For those of you that don't have MGS2:SOL -
What are you waiting for?!? Get this game now. It is easily worth the $50 price of admission. You'll basically be getting 2 games (at least) for the price of one. Having played Splinter Cell, I'd argue that SC bosts better gameplay and graphics, and it also has that "fresh" quality to it that you won't find here. But in terms of sheer value, I think Substance will be the winner. Anyone who likes stealth action owes it to themselves to own both games.
Once I get a little deeper into the extra missions, I'll provide more updates. Also if anyone has any questions, fire away!
This Novemeber, Xbox is a stealth action fan's wet dream. Between Hitman 2, Splinter Cell, and MGS2:Substance - I think I've died and gone to heaven.
Vivan los portes baratos... por lo menos parece que en otros aspectos mejora ligeramente.

