If you never played any of the other MGS games you really should before diving into this one (the story features heavily in these games).
There is indeed a lot of cutscenes (not cgi mind you, none of it is cgi) but they have small amounts of control that let the player involve themselves more. Such as looking through first person and so on, keeps things lively.
I can safely say this game is way better as far as the controls go, the old games controls were kind of complex (especially for a casual gamer). Not so much any more.
MGS4 is easily the best reason to own a PS3, you really are kidding yourself if you don't own it but have a PS3 sitting there.
If you need to catch up with the story-line, I hear they just did a free update that lets you read up on the story so far from the other MGS games. Either that or go buy the compilation and run it on a PS2, only costs about 30 bucks.
But yeah... excellent game. I'm going to have to stop bumming off my friends PS3 and actually go buy one for MGS4.