As others have mentioned, this is a tiny game, with the main story line taking perhaps one hour to complete. However, it has some mini missions, and the main story is quite re-playable. There's also a little bit of plot with some exciting cut scenes.
The gameplay is smooth and intuitive, and the scenery looks incredible. Snake moves pretty well, and this is an example of in-game cut scenes really done well, with characters that interact properly with each other and their surroundings.
The only down side (apart from the incredibly short game) is having Kiefer Sutherland as Snake. They have done this to make this game grittier and darker, but Sutherland must have been busy or expensive when they were booking him, since he hardly ever speaks. Everything the player needs to know (like take out that guard first, check your iDroid, etc) is voiced by a helpful friend in your ear, and Snake never says thanks. If you enjoy games like Uncharted where the main character is constantly muttering to himself, or makes a little noise when he drops off something high, don't get your hopes up here.
This lack of vocals, plus the very short run-time, are the only things that stopped this being 5 stars.