This is one of the most complex games to reviews since there are so many different avenues to examine it from. I guess it's important to start out with the basics.

First, the gameplay. Metal Gear Solid 5 is indeed what everyone has called it: one of the best stealth games ever, providing the peak of what the genre has to offer. The amount of player freedom, the choices of lethal vs. nonlethal play along with chaos vs stealth, and the massive arsenal of tools at your disposal are all facets of the gameplay that make it stand out as one of the most fun, addictive, and pristine gameplay loops out there. Personally, I found doing everything Nonlethal (except for that one... mission) and Stealthy was more fun than doing things Lethal and Loud as it made capturing outposts, recruiting soldiers to Mother Base, and completing the Main and Side Ops incredibly rewarding. And honestly, the controls are pitch-perfect.
Speaking of Mother Base, while the base itself doesn't have much to offer, the pure satisfaction from growing it through building new platforms and recruiting the best S Rank soldiers you can find is the true goal.
The Buddy System is also an excellent system with each companion having their own unique abilities with D-Horse who arguably is the least useful companion aside from alleviating wandering the open world slowly, D-Walker that can be customized for offensive and defensive combat, D-Dog who can stun, distract, wound, or kill enemies on command, and Quiet who can serve as extremely useful sniping power and covering fire. D-Dog and Quiet ended up being my favorite Buddies to use because of their fun endlessly helpful mechanics. (Also, as a side note, yes, Quiet is shamelessly objectified despite what Kojima has said otherwise. The excuse for her objectification with her only able to breath through her skin and photosynthesis is such a thinly-veiled justification and by the game, you just can't buy it anymore. So yes, Quiet's appearance did not have to be this way and I'm sorry if I'm wrong for pointing it out in the first place. Thankfully, the game allows you to give her two fully-clothed uniforms which are SO MUCH more fitting for her.)

Secondly, the story. Yes, there's no doubt that it's one of the main issues with Metal Gear Solid 5. It's definitely the weakest story in the main series with unfinished plot threads such as Eli/Liquid Snake and hijacking Sahelanthropus, underdeveloped ideas such as Skull Face and his agenda (I thought he was incredibly underwhelming compared to every other antagonist), and forced and contrived concepts such as Psycho Mantis and the Man on Fire. In particular to this last aspect, both characters feel like fan-service in the wrong way in comparison to Metal Gear Solid 4 which was fan-service done right and to its most extreme.
There's also the major plot twist with Venom Snake not actually being Big Boss which initially seemed like a sudden and half-baked twist, but after thinking about it after fully completing the game, I actually grew to accept and even like it. It felt like Hideo Kojima truly said goodbye to the series and his fans by saying that we are or can become a legendary soldier in the world.
Regardless, Metal Gear Solid 5 IS the weakest story, but to quote the words from Max Derrat on YouTube, "a poor Metal Gear Solid story is still better than most."

Lastly, the production of this game itself. It's hardly a secret that the troubles between Hideo Kojima and Konami resulted in Metal Gear Solid 5 being compromised, to say the least. With the discoveries of a lost Chapter 51: Kingdom of the Flies, the existence of repeated missions, and the somewhat rushed ending, it's really saddening and disheartening to see the last true Metal Gear game be like this. I have nothing but sympathy for Kojima and his team with what they went through and Konami should forever remain ashamed of themselves for prohibiting the man's ideal vision and for betraying the trust of their fans through Metal Gear Solid 5 and its treatment towards their other IPs.
And for those that argue that the game being incomplete strengthens its themes of loss, revenge, and phantom pain, I thoroughly understand that sentiment.
However, you can explore those themes of incompleteness while also providing a complete experience at the same time. Konami just shot themselves before they could do that.

Despite the controversies surrounding this game, I had a lot of fun with it and I'm grateful for my time with it. Welp, that's all! Time for Metal Gear 1!