Well, let's just say that you can forget about story in Phantom Plot, while MGS4 is more plot than game. Hope it makes sense. Don't think you'll be disappointed by 4, play it. PP is, mechanically, is pretty great, but the story is just is not there.
That's my take. I used to be a fan like you, then PP kicked me in the balls...
Oh, yeah, you probably already know this buy stay the fuck away from Survive..