I want to play only one MGS game

>I want to play only one MGS game
No, you do not.
You NEED to play them ALL, in the RELEASE ORDER.

If you MUST sample just one, it NEEDS to be the MGS1. It is a crucial chapter in the story, and a magnificent game.

You're practically asking "which book of the Lord Of The Rings should I try, because I dun wanna read an entire trilogy! :^)))".
AKA: autistic as fuck moron.

>I want to know which one I should play alone.
NONE OF THEM, idiot.
It's a linearly progressing series, with each new title assuming that you have played the previous games already, and only building on top of it.

>each new title assuming you have played the previous games already
That's a lie user. 3 is almost removed from the overrall narrative.

You do not get it.
All the MGS are more or less fine games as-is, but the real reason why the SERIES is so beloved is its decades-lasting lore and re-occuring elements between the episodes. Not only are you following some legendary characters go through some crazier and crazier events as they grow older, but (You) yourself travel with them, with your own actions becoming part of the experience.