I think you are somewhat underestimating this game, onimusha.
Yes, it has that weird thing where it focuses heavily on cinematics as well, but seeing how I've seen (on a forum in my country) that a LOT of people who have never played MGS will now buy the game, it shows that this game will appeal to a broader audience than before.
And a broader audience means that more people will hear about it from friends. And after a couple of weeks, I don't think it's the hardcore gamer that still needs convincing whether or not to buy this game; it'll be the mainstream gamer who is going to doubt whether to buy this game or not.
Consider then the visuals, the presentation, the multiplayer ability, the mouth-to-mouth advertizing, and the fact that you could replay the game to play it in another fashion (attack straight on - stealth - average), would make it more accessible for a larger audience, meaning it'll appeal to more people, creating longer legs.
Hell, even I couldn't care less about MGS and I'm interested in this game, even though I don't have a PS3
