It's the Far Cry 2 of Metal Gear Solid games. You wander around Africa clearing outposts, listening to audio tapes, and collecting diamonds. Missions are designed in a way that largely respects the sandbox. It doesn't shove you into an arbitrary set of rules every so often. If you're told to extract a hostage, you can do that however you want.
Incidentally, also MGS V owes quite a bit to Pandemic's Mercenaries. But its utilitarian approach to world design and the use of overlapping systems instead of explicit scripted missions is pure Far Cry 2.
During the development of the original Splinter Cell, Clint Hocking and some of the developers squabbled over the proper direction for the series. Hocking wanted player freedom. Hocking wanted players to be able to go anywhere, come at a problem from any angle. The other side wanted a linear series of set pieces because Metal Gear Solid did that and they wanted to make a "Metal Gear Solid killer". But in the long run, Hocking had the last laugh because Metal Gear Solid turned into a hybrid of his two games -- Chaos Theory and Far Cry 2.
I don't think it's worth losing sleep over Metacritic. There is something to be said, however, for how insane waves of hype around certain game series with high levels of prestige attached to them cause a certain sense of myopic adoration.