Until the game releases and everybody suddenly becomes 'realistic' the greatest game of all time ever is obviously BioShock: Infinite. Unless you hated BioShock 2... anyway, there's a video that is being variously described as... "Awesome", "Eyepopping", "the best pre-release game advert video ever", "much better than Meh" and other things. It's introduced by games industry spokesman, Geoff Keighley.
You should watch it, make up your mind about how great the game is and then argue with other people.