Still, I am curious why people seem to like it for the most part. I refuse to believe that most people enjoy walking simulators, so there must be something to it that makes it more than that.
There is definitely a lot more to it, but I don't think a lot of folks make it past chapter 2 (the first two chapters take place in the intro area, which is, well, boring). After that there's more interesting biomes, vehicles, story, characters, road building, expanding your gear and network, stealth/action, bosses, etc. I found it surprisingly refreshing. Replayability value is low though. And if you don't like 20-minute cutscenes followed by another 20-minute cutscene, looks elsewhere, this game is no different than the last few MGSes for that matter. And there are a questionable mission or two in there that force you to walk and do a crapload of backtracking.
What made it tick for me is the weirdness, chillin' in a beautiful environment and the slow pace, it was a welcome change. The walking simulator (or rather: dynamic load simulator) part is surprisingly fun too, you really need to plan every step you take, especially in rough terrain. Oh, and typical Kojima cheeky humor (also: typical Kojima cringy dialogue some times).
Definitely not for everyone though, it's too niche to be mainstream. (Which I find great, but companies need money in the bank to make AAA releases.
).