Well I have already played and beat 5. I had no idea what was going on most of the time and then google told me all the Metal Gear games are like that. I still had a blast with it though. There is no way I am going to buy all the metal gear games. I would then have to figure out which ones will play on my PS2 or PS3 and track them down. Too much work. There are just way too many games to play on PS NOW and Game Pass that I have already paid for sub wise. Someone wouldn't watch only Endgame since all the Marvel movies are on Disneyplus. It's not like all the Metal Gear Solid games are on PS Now and I am choosing to only play 4. It's either play 4 before it leaves in 12 days or not play it at all. Since it's gotten amazing reviews, I am choosing to play it. I got to the guy that trades weapons for points before saving and putting on the Penguins game. I will play a lot more tonight.
I beat 5 without playing Peace Walker and I thought I didn't miss out on much. 4, however, references past games as it is the culmination of their stories. Then again, MGS stories are wack and you probably won't connect everything together unless you watch a lore video. My friends dragged me to watch the last Harry Potter movie opening weekend and I had never seen any of the prior movies so I didn't get very much out of that experience. But anyway, if you do choose to play 4, I think the game is worth a replay after you've had time to play the other games.