Playing Ground Zeroes right now. I don't even think I've ever played one of the prior installments in the MGS series.
I'm sold on the Phantom Pain off the strength of this demo, though.
The game play is smooth as hell and the different ways to accomplish your mission keeps it fresh.
Can only imagine how fleshed out the retail game will be given the scope, size, and equipment at the players disposal.
I'll browse the wiki to try & catch up to the story & screw Konami for cancelling Silent Hills, but they've got my money on this one.