Picked up Subsistence today, and spent some ample time with it this afternoon.
Disc 1 / Subsistence: Basically the original Snake Eater, with the newly-added third-person camera. The new camera is, for the most part, a delight to play with, and puts a fresh new take on the main game. It's a bit disorienting at first, but once you get the hang of it, it makes scouting ahead to see on-coming enemies much easier. The additional freedom of being able to explore your surroundings, and 'set' your own angle of the action is a neat new perk for a game as graphically-intensive as Snake Eater. You still have the option to revert to the old camera on-the-fly, and the fixed angles do help in a number of places. Gameplay-wise, the core mechanics remain unchanged, for better or worse. Doing pop-out shots, for instance, remains largely useless, due to lack of a decent auto-aim, and really slow reaction time on the pop-back.
Any codec-radio and sound lag problems that plagued the initial U.S. release (which was subsequently fixed for all other versions afterwards) has been fixed, and general loading between the Survival Viewer and menus seem a bit speedier overall.
There are lots of new camo uniforms and facepaints, most of which are for novelty purposes, already at your disposal from the very start. The only catch is that you have to "download" the majority of them to your memory card, via the "Special" menu at the title screen - and each camo is a whopping 850+ KB in size. There are approximately 20 new uniforms, in addition to the ones that are in-game which you need to find, or earn by defeating bosses. Also, Japanese-specific unlockables from the original Snake Eater are already available to you, such as the Auscam, Flecktarn, and Desert Tiger. Very cool.
Disc 2 / Persistence: Where the main online game resides, as well as the bulk of all the extras; the MSX ports of Metal Gear and Metal Gear 2: Solid Snake, and MGS3's single player bonus modes. Snake Eater's data is incompatible with Subsistence's, so that means having to play the game all over. Also, difficulty levels don't carry over for each play through, as to my understanding, much like the original SE; so that means once you choose a difficulty level, you have to stick with it for multiple playthroughs. On the plus side, choosing the new option "I like MGS3!" at the very beginning of the game on disc 1, and then creating a save file opens up all of Subsistence's single player bonus features right off the bat, including Duel Mode, Demo Theater, extra Snake vs Monkey levels, the Secret Theaters, and all difficulty levels (including European Extreme.) First time players may want to hold off on that until beating the game themselves.
All of the Secret Theaters that were initially available online are all archived here, along with a number of new ones - and dubbed completely in English. Metal Gear Raiden: Snake Eraser is worth the price of admission alone, and they even got Quinton Flynn to do Raiden, and Lara Cody for Rose! Very, very cool.
I've tapped into the MSX titles only briefly, but they look to be port-perfect. The controls have adopted to the Metal Gear Solid style, so now L2 and R2 shifts through the items/weapon inventory, Square is the shoot button, Circle is attack, etc. I'm looking forward to seeing how the new script translation turned out, in particular.
I'm saddened that I can't participate in the online modes, because from the looks of it, people are having boatloads of fun. Maybe that's a good thing, though; tempting as it is to become a MMO junkie for a game I feel so passionate about, I just wouldn't be able to afford the time. With the exception of not being able to move and shoot at the same time in first-person mode (and reports that hosts are sometimes discriminatory sore losers by kicking players out of play sessions) it looks like Metal Gear Online, for the most part, is a rousing success.
Disc 3 / Existence: I've yet to actually check out this Limited Edition extra, which is essentially a three and a half hour movie edit that Kojima put together, comprising of Snake Eater's cutscenes, codec dialogue, in-game footage and a newly added narrator. Only thing I can say about it so far is that it is indeed a PS2 disc, which means you can't play the movie on a regular DVD player. Peh.