I NEED SCISSORS said:
It was actually meant to be the last in the series, before Kojima went into permanent drama queen mode and Konami forced him to make more he couldn't let the series go.
Pretty much. The whole thing gets more and more ridiculous, layering insane conspiracies on top of each other, frustrating your every expectation at what Metal Gear is supposed to be, and every time Raiden (the player) asks for an explanation, Snake just says, "Dude, it's up to you. Take what you want, and pass it on." MGS2 basically begs the player to stop taking the events that occur in it seriously.
And then everyone said, "Kojima, please tell me what to think! Please tell me what happened!" And even though he had said
during MGS2's development, "This is my Metal Gear and I can destroy it if I want to," he just had to keep going, because people kept asking for more from him. Even when he answers all their questions, they are never satisfied.
It's sort of sad, in a way. Someone posted a link to a
big analysis of MGS4 in the official thread here, and while the whole thing largely consists of pointing out every moment in the game that references every other moment in the Metal Gear saga, the overall thesis seems to be that a franchise shouldn't continue indefinitely, because its reliance on its own tropes prevent it from creating something newer and better. If we assume that this analysis captures Kojima's intent, the entire message of MGS4 is that the Metal Gear series needs to die.
Next year, Metal Gear Solid (5?): Peace Walker is announced.