Words are simply insufficient to describe the colossal sense of WIN which this game engenders in fans of the MGS saga, therefore the only useful response is a visual representation of said fans' reactions:
FUCKING WIN!!! This shit is awesome! It is made of WIN and GOD! (and yes, that's me in the photo)
Yeah, I know I've used the sentence above more than a couple of times already, but really, it couldn't describe MGS4 more properly. This game is the shit! This is next-gen! The current generation is filled with great games, that's undeniable (unlike what some people say...), but lets be honest, despite prettier graphics most of them don't really feel like their the next generation of games, bur rather the same old games with just new make-up. This game, on the contrary, is next-gen in everything it does, and it would be simple impossible to do without the modern hardware.
Yes, this is so far the pinnacle of HD gaming, and is more than enough reason to buy a PS3 just for it. No, I'm not insane, I just fucking love the game! The graphics are just "OMG awesome". The animations? Even better. Gameplay? Just fantastic, still fresh even after 4 games and polished up to near perfection. Sound? Unbelievably good. And story? The story is the best damn part! We get to see practically every character from the series again (except the dead ones, obviously) and finally we have answers for the questions that tormented us for so much time! What happened to Olga's daughter? Why the fuck is Vamp apparently immortal? And why the hell does Snake look older than my granpa? Patience, young padawan, for all this will be answered in this most excellent of sequels.
So, what the hell are you doing here reading this? Go play the damn game. Now!
Just for the record, I'm not finished yet, I just reached Act 3, so be careful with spoilers when commenting, ok? :)