Basically Hideo Kojima tried to combine Journey, Monster Hunter, Survival games, Dark Souls' soft MMO mechanics and MGS into one giant game where you're a UPS delivery guy.
>The game has crafting mechanics where you collect resources plus points to build items, vehicles and buildings you can place around various maps for either you to use, or other players can use online. You can also leave helpful links, or troll messages for other players to read.
>The game has random encounters against minibosses, which can be avoided, most of said minibosses however are bullet sponges except for the occasional animal based ones. Storymode bosses are almost all animal based, and are basically Monster Hunter bosses but with MGS5 shooting mechanics.
>The game has random sections of the map where you'll see rival factions and you'll be given the option to sneak past them or go rambo against them. However just like MGSV proved, Kojima sucks ass at making openworld stealth, so cheesing the enemy AI is really fucking easy. The regen health and "mother base" style upgrades you can get also make most of the fights pretty much a breeze to slam through.
>The game has random encounters with these ghost like apparitions, in which you can easily stealth yourself out of, if you're not careful they'll either trigger the bullet sponge miniboss fights, or a game over.
>The game design is vast and takes advantage of all the platforming mechanics and metagame mechanics. Things like how heavy the packages you're carrying around affect the way you traverse mountains, ford rivers, cross bridges made out of ladders and so forth. Certain shortcuts can't be taken advantage of by vehicles, but are dangerous if you're carrying too many shipments. Combat and sneaking around is really just the inbetweens, the real fun is in the platforming mechanics and discovering shortcuts or exploiting game bugs/mechanics to get through platforming obstacles.
This game is a very interesting mishmash of ideas, it is unironically Kojima's most ambitious game yet. But inversely said precisely because it's a combination of so many unconventional ideas it can be very off putting for many players who just expected a mindless platformer, a straight forward survival game, a sneaking/espionage game, or yet another generic cover based third person shooter. The story, I can't judge the story, I've only watched around an hour's worth of gameplay footage because Kojima hasn't written a good videogame story since MGS