If we speak about pick up a game without any knowledge even from friends etc... It's probably Metal Gear Solid for me.
My father wanted to buy me a game, we went to the supermarket. I didn't really know what to take. I saw this game, looked the back of the box. It read like a movie so I took it.
My father : "You sure you want this one ?"
Me (not so sure) "Yeah yeah" .
Was blown away just with the intro. It changed my vision of video games...
There is probably other I took without much knowledge but can't be 100% sure (mainly old stuff like Half-Life, FFX)
Nowadays I don't necessarily check heavily each game I buy, but I usually always check a bit of gameplay to get a feeling.