The game consists of two parts: one where you play Solid Snake aboard a tanker transporting a new type of Metal Gear, and one where you play Raiden, a member of FoxHound sent to an environmental cleaning installation that was built on the site where a tanker went down a few years ago (!).
The decision to have the players play as Raiden was a controversial one -- apparently Hideo wanted to show the Snake character from a different angle. And that worked pretty well, we see Snake as this ultra-competent soldier, while Raiden is tasked with the petty work. I enjoy Snake more as a character, but I don't think Raiden deserved the loathing he received from the fans.
The first part is typical Metal Gear, and quite linear. But the second part makes the most out of the environments: you traverse the Big Shell quite a few times for various reasons, and the fact that it is circular allows you to choose multiple routes, which I liked quite a bit. The environment is large, and you do traverse some parts multiple times, but the 'compactness' of it makes it that you can easily get from one place to another without taking too much time.
The villains... I didn't quite like 'em. You only ever really fight with Fatman. Sure, there are a few bouts with Vamp, but he never stays dead -- so he doesn't ever get to do his farewell speech.
The storyline is as convuluted as humanly possible. Once again, the Patriots are the bad guys who secretly pull all the strings behind the scenes -- layers upon layers upon layers. All of this needs lots of exposition, hence the long cutscenes. And in the end... I just couldn't care anymore, really. I just wanted to complete the game so that I could go do something else.
The supporting cast isn't that great, either. OK, Otacon who starts using Chinese proverbs is pretty amusing, but Rose's incessant whining really got on my nerves. Also, Otacon just isn't the right person for melodrama.
The ending is another one of Hideo's rants about life, the universe and everything. Nothing we hadn't already heard at the end of MGS1. But then Otacon tells us that he found the list of the Patriots, hidden deep in GW's code. First he tells us that one of the Patriots was a major financial backer of the anti-Metal Gear foundation he and Snake spearheaded, and then he tells us that they all have been dead for over a hundred years! Which is it, Otacon!?
I think that Metal Gear Solid 1 (the one for the PSX) is the best game out of the whole franchise. It re-invigorated the series with a fresh new appeal. Boss battles are nicely spaced out, and the hardware is really pushed to the limits. As usual, the story is convoluted and there is some betrayal going on, but it is all broken down to managable proportions. The boss fights are interesting and exciting, and spaced just right.