The game is only 4-6 hours long, but like Vanquish, it is fat-free with basically no padded material, so you could easily play the campaign multiple times (they also offer some in-game incentives for the completionist types.) Still, if you are just interested in blowing through the campaign once, I suggest either renting or waiting for a large price drop.
I thought the gameplay itself was pretty fun: the camera is a bit sticky in place, but the parry system was interesting. Free-cutting is pretty much entirely a gimmick but it’s pretty fun to fool around with. The story is stupid nonsense… I know MGS isn’t exactly Shakespeare, but I was not happy that they made this a quasi-sequel to MGS4. It’s too violent and off-the-wall for MGS (Raiden can throw Metal Gear Rays!), and even though it has a mostly dark and serious story throughout, the final boss ends up being super goofy.