I think the the bigest trouble with this game is that the trailers sold the game as the path to hell that showed us how snake became the big boss from the first metal gears, and even without taking into account the real ending of the game, this never happened, making the expectatives from people like us who enjoyed the story series way too higher.
Also, some people took the way on how Konami treated Kojima way to seriously, making it easier to criticise this game (which has his flaws mind you, specially since is a radical change on how the previous MG were portrayed)
With that being said, I enjoyed the game, even though the open world was not that rich, I still enjoyed traveling through Africa and Afghanistan, the missions could get repetitive but I still enjoyed mastering all the camps, it's true that after some point you don't had the need to be hide at all, but it was cool that you had lots of ways to solve problems, also was cool to see how the mother base growth, even though at times it felt like a grind.
And heck, I enjoyed the story, the pace was terrible and the disorder on how you unlocked the cutscenes was awful, but I liked this idea that you were an outlaw who had to do the dirty work for other organizations, while searching your personal vendetta, and the ending was an ok explanation on why happened some events in the first metal gear, still I think that they could have detailed some things better.
In the end, this is one of my favorite games ever, I hardly put 100+ hours on a single player game, just for that, I can't really hate it