So apparently it's like 2 hours worth of gameplay, seems that people are not amused with that. All that being said I'll likely still give it a play since I'm a huge MGS fan, though I wouldn't drop $30 for it.

Well they all follow a linear story, so you need to start at the beginning. I haven't started Ground Zeroes yet, I plan to play though the short prologue sometime this week hopefully, as from what I understand it's only about 2 hours long. They are all great games though, I love MGS.