The presentation did go out of its way to emphasize that Snake is the only hero in the game, so any Raiden fans out there can give up hope of seeing the blonde one's return. When prompted to expound on the game's story afterward, Kojima was quite mum and said only that more would be revealed next year. Further, when GameSpot's Giancarlo Varanini asked Kojima where on the timeline this new Metal Gear game falls, Kojima would answer only that we should use our imagination. This, coupled with briefly-glimpsed phrases during the trailer such as "Back to the origin!" and "1960s" has led to speculation that Snake Eater may in fact be a prequel to the series. Indeed, Solid Snake's age has been called into question as some members of the GameSpot staff believe he is far too young to appear in a game set in the 1960s. Of course, this depends on the game being set in the 1960s, which itself is a fairly large assumption to make. If we've learned anything from MGS2, it's that we should expect the unexpected from Kojima. Only time will tell if we've made an accurate assessment of the situation.
And now DOOMSpot (My impressions ):
Story/Setting I'm very excited to see Metal Gear back in the jungle! A lot of people will claim this to be a first for the series, but in actuality only 2 out of the 5 Metal Gear games were placed entirely indoors. And who's to say this isn't just for Insertion (like with the original Metal Gear). I'm really excited about the whole jungle combat thing, as I'm getting kinda bored of 90 degree wall indoor battles, especially if Camoflauge plays a part in how the AI reacts (or doesnt' react) to you!
As for the story, things seem to indicate that this game is actually set in the 1960's. Also look at the weaponry used and also the technology. Not very high-tech looking binoculars Snake (or whomever) was using. Same with the sniper scope. And also if you look closely, you'll see a wire going to Snake (or whomever)'s ear, assumingly for radio communications. This means no Nanomachines like in MGS1&2 (and Ghost Babel). All this indicates that the game takes place in the 60's, cold war era.
Which means that, unless some foolery is taken with the entire Metal Gear storyline, you're not really playing as David Hayter, aka Solid Snake. My Theory? You play, at least in the parts of from the trailer shown here, as Big Boss. After all, Snake is a clone of him, so he should look similar. Also, someone in the other MGS3 trailer pointed out that this Snake only has one eye, an attribute Big Boss had. Big Boss supposedly was operating in the 60's and thus probably in his 20's or 30's. And in MGS2 its stated that Big Boss was in his 50's when Solid & Liquid were cloned. Also, just by seeing how this Snake runs around, he's a whole lot more bloodthirsty and willing to kill people than the almost pacifist Solid Snake we see in MGS2.
My personal hopes for this game? I hope only a very small part takes place in the 60's playing as Big Boss, kinda like how it works with the Tanker plant in MGS2, and then have the rest of the game as something else, with David Hayter being THE Snake, in a time past MGS2...
Also the kinda techno-ish tomfoolery of the trailer itself has me a little concerned... I hope Metal Gear didn't go down the toilet. Again...
Gameplay This has me really, really excited. Finally, Snake gets to use a knife and STAB STAB STAB! The hanging while shooting thing looks cool too. However, I think the coolest possibility is that hopefully the camo you are wearing actually hides you from the AI, so you don't necessarily have to be not in their cone of view to avoid detections. This could allow for some very cool Rambo-ish back-against-a-tree-till-they-pass-then-STAB-STAB-STAB moments!
Also, something in the trailer that I found to be quite hilarious is the GTA Vice City references, and also when Snake holds the guy hostage demanding a release date. heh.
 I was taking some zoomed in shots of the screenshots mentioned above, when I saw something very interesting:
Clearly, in the first shot Snake (or Big Boss?) has TWO eyes, but in the later shots it looks quite a lot like he has lost his right eye. Leading me even further to think that either these are two different Snakes, or the game is at least in part in the 60's with Big Boss... [/edit]