Very good story (for first time playing through) and great multiplayer.
Great story, and really fun. Although the scenes are extremely long (not exaggerating), the first play through deserves your full attention. Not only do the graphics look amazing in game cut-scenes, the loading between cut-scenes and instant-action is not there at all! Sure there is loading, but not when you are about to go into a huge battle.
Multiplayer (MGO)
Very fun, but a little pain. Sure it's fun, and very satisfying to get kills, but registering and logging in really is a pain. Basically, how this works, your PSN ID means nothing here! You have to make two seperate accounts! One is a Game ID, and the other a KONAMI ID. Once you are done, signing-in feels as if it was a PC game. That is not cool. But the gameplay is great!
I'd say buy. I owned two XBox 360's, one of them catched RRoD, so I traded it in for a PS3, since MGS4 was already out, and I have never looked back.