Peace Walker is criminally underrated, it was very easy but Co-op Metal Gear is just way too much fun and I hope it's in Ground Zeroes/Phantom Pain.

MGS4 is still an incredible game to me if only for the insane and imaginative art design and the most fun 0 kills 0 alerts play through. I also enjoy just how diverse each section is from start to finish. It still has that palpable "next gen ambition" that I feel a lot of developers lost as we got settled in to the cycle.

The great gameplay also birthed Metal Gear Online, which was way ahead of its time and one of the most unique multiplayer titles of last gen.