The first hours of the game are excellent. The prologue swiftly creates an intriguing and mysterious atmosphere and the gradual discovery of gameplay elements is incredibly rich, we weren't bored for a second. The level design for every mission is very well done, the total freedom offered to the player and a sound track which always highlights and amplifies the sensation of danger greatly helps immersion.
You're not merely controlling Big Boss, you are Big Boss! But, as the game goes on, a sensation of repetitiveness grows. This is due to three elements : a "special" gameplay, an open world which doesn't feel totally mastered (->finished, well used), and a very diluted narration. The well-known gameplay (Peace Walker) means you're alterning between ground missions and base managing. You've got to recruit soldiers and assign them to diverse tasks in your HQ to develop new weapons. The problem is that the gadgets and arms which allow to easily kidnap these soldiers are developed at a very slow pace, while lethal weapons are very quickly acquired, but are more or less useless. Furthermore, the HQ development implies that a lot of side quests need to be completed, without which the player can find himself stuck in the main quest progression as he will not have unlocked the necessary gadgets. This difficulty often pushes the player to grind levels, as if this was a classic RPG, through the repetition of missions. If this wasn't much of a problem in Peace Walker, as game phases were shorter, it quickly becomes tedious in MGS V as the environment is much bigger.
If you ignore the few plants that you can collect here and there, or the animals you can send back to your HQ, the game doesn't really give much in terms of side content. The side-quests are very similar to the main quests, and the game is always concentrated on camp infiltration. So there isn't much in terms of gameplay variety, except for the freedom in the methods that you choose to employ. But, compared to Witcher 3, or Batman:AK, which both propose a lot of very diverse activities, MGS:V feels more limited. However this uniformity in the gameplay has always been a part of the series, and was always well supported by its fascinating plot and cast, which always made the player want to advance in order to discover more. On this point, MGS:V is confusing. After an incredibly good start, cinematics suddenly become very rare and the plot doesn't feel like it's advancing.. until the very end.
Most of the questions/problems put forth through the adventure aren't solved by the end (there is no resolution to them) - which leads the player to interpret the game his own way, except of course if a secret, real ending exists that we have not reached.
Once the game is finished, we can indeed repeat old quests, in a harder setting (examples : unarmed, undetected, etc).
Some side quests prolongate the main story and unlock new cinematics.
It's all very confused, and, after having reached the end of the game, it becomes a bit tedious to have to repeat and re-repeat so many missions, go back to the same old areas, etc... just to unlock new material. But this is reminiscent of MGS Peace Walker, so MGS fans shouldn't be too surprised.
MGS V is still a fascinating game. Even if the game only puts forth infiltration missions, there are so many different ways to accomplish them that we always stay surprised.
Once players have unlocked all the tools at their disposal and learnt how to use them, infiltrations become very easy. Until then, players must accept to die a lot and start again, in order to realise a clean and proper infiltration. The partner system takes a long time to show its interest, you must stay patient as the trust levels slowly grow, allowing for more interaction with these partners. MGS:V is a game which should be played patiently; rushing it will probably lead to boredom. The construction in episodes (there's an intro and an outro to each mission) supports this idea that the adventure should stay gradual and can be picked up again at any moment. This is why the accent is put on the gameplay and the "infinite" ways of action, while the story-telling takes the backseat. It still feels like Kojima is backstabbing us with this opaque, unclear, methaporical story, which finds no closure - unless, once again, a secret ending exists. Finally, what if the real surprise with MGS:V was how it doesn't conform to the idea we had of it ? A risky move that could confuse more than one player, starting by us.