Even keen students of Metal Gear lore are going to struggle to follow this tangled tale. Laden with sentimental sermons and metaphors for the evils of war, struggling under the weight of the resolving the plots of four previous games and the personal destinies of characters as diverse as Raiden, Meryl, Naomi, Vamp and Eva, it is in all honesty a mess. Motivation and consistency fall by the wayside and by the end it's totally unclear who is on which side, or what's at stake. Maybe that's deliberate, but it doesn't work, and the hours of talking-head exposition involved are too steep a price to pay for this muddled closure.
But that's just the plot. There's another side to this story, and it's the one told by the game's locations, action and dramatic high-points - and in some cases, by moments between its handsome, expressive and earnestly-voiced cast of virtual actors. This story is, by contrast, a richly satisfying success. Tune out the details, and Guns of the Patriots is a properly gripping yarn, full of thrills, spectacle, laughs, and even tenderness and pathos. You won't understand, but you will care

关于剧情就这两段，你来讲下大意呢