According to an article in Game Informer magazine, the story campaign for next month's Metal Gear Solid V: Ground Zeroes is going to be really, really short. As in two hours short.
Game Informer writes (via Kotaku): "Judged just by the core story mission, Ground Zeroes is short. We completed it in just less than two hours."
Your actual mileage may vary, since as the article notes, the demo lasted four hours: enough time to play through the main mission and experiment with extra modes. And length doesn't necessarily have any bearing on the game's quality. MGSV is already being sold at a slightly reduced price compared to standard releases: Xbox One and PS4 will cost $30 for a digital download or $40 for retail, while PS3 and Xbox 360 versions of the game will cost $20 for digital and $30 at retail.